Before I go into a detailed response to everything you mentioned, let me just say that the source that you are quoting is essentially a part of an intellectual feedback loop that includes the creator of Refold. Matt and Professor Brown are both subscribers to the ‘input hypothesis’, which was created by Stephen Krashen (who is interviewed in the video) about 40 years ago. Research on second language acquisition has since analysed this theory and moved past it, as I mention below.
That’s an oversimplification of the monitor hypothesis, which is actually a part of Krashen’s theory of second language acquisition, which is a set of five hypotheses collectively known as ‘the input hypothesis’, which is actually the name of the first one. You can take a look at the Wikipedia page if you want to know more. The ‘monitor hypothesis’ is the third hypothesis. The ‘monitor’ is in fact a neutral concept that expresses the idea that a learner can use learned knowledge to correct himself. However, it’s true that the Wikipedia page (which relies on Krashen’s writings) shows that Krashen feels that using the ‘monitor’ is a difficult process, and that it’s best not to rely too much on it. This doesn’t just apply to grammatical knowledge, by the way: the assumption is that there’s a huge difference between ‘learned’ knowledge and ‘acquired’ knowledge (I believe ‘acquired’ knowledge, according to him, is basically subconscious/doesn’t require thinking to be used), and that what is learnt can only be used for checking, and not for actual output.
However, this hypothesis has faced criticism over the years. First of all, Krashen’s entire theory has been criticised for a lack of evidence, the input hypothesis in particular (A Critical Review of Krashen’s Input Hypothesis: Three Major Arguments). Secondly, the monitor hypothesis itself is problematic: ‘learning’ and ‘acquisition’ have been found to be difficult, if not impossible, to separate, challenging one of the fundamental premises of the hypothesis. Furthermore, the hypothesis assumes that what has been consciously learned cannot turn into output, whereas learners everywhere undoubtedly do use consciously learned knowledge (like known grammatical structures or vocabulary words) to help them form sentences and understand language used by others (The Monitor Hypothesis: Definition and Criticism - LinguisticsGirl). Perhaps far more importantly, Krashen’s theory is very old and has since been superseded by other theories. Here’s a post on another thread that discussed the input hypothesis: Is Matt's (from Matt vs Japan) idea--that it's more efficient to go more reading heavy before going more listening heavy--consistent with your experience? - #30 by nclbk
Finally, here’s a Word document that cites several criticisms of the monitor hypothesis. It’s from this website, on this page which tackles approaches to second language acquisition. The most prominent counter-argument cited, to my mind, is the fact that ‘good learners’ tend to be the ones who pay attention to both meaning and form (i.e. exactly what Krashen claims is so bad/harmful for fluency). However, in all fairness, the author of the document points out that these assessments were made in an academic context, and that as such, the criteria for being ‘good’ may favour structured learning and grammatical knowledge.
Here’s a thread that discussed this very video. I was on it, and so if you wish/you’re tired of my arguments, you can certainly ignore whatever I’ve said there, but there was quite a bit of criticism of Professor Brown’s claims, including the fact that he did not seem to have adequate comprehension and that he made pronunciation mistakes that were ‘painful to hear’ by using ‘the wrong letters’ (i.e. it seems he wasn’t simply imprecise, but made sounds that sounded like other Arabic letters altogether).
I did not claim this, and I most certainly did not claim that all types of grammatical study are helpful. I gave specific examples of how I use grammatical knowledge to help me learn more quickly, and it’s quite clear that what I do is much closer to acquiring knowledge of linguistics within a language than what is done in most textbooks. For that matter, I’ll allow myself to cite a member of WK who knows far more than me about SLA:
In other words, grammatical instruction can be helpful, but traditional grammatical instruction may not be. Furthermore, studies have shown that explicit grammatical instruction does not produce better output directly in the average learner:
However, again, these studies certainly had to examine some method of grammatical instruction or other, meaning that this only proves that, once again, traditional strategies for teaching grammar don’t work very well. (Note that the conclusions of Benati et al. cited above are significantly more recent than the study from Macaro & Masterman.)
In other words,…
Yes, this is true. I’m not denying that. However,…
…exactly how much confusion this generates is a matter of attitude as well. At times, it simply means that the real ‘rules’ – the most prevalent patterns of usage – are actually more complex than what was detailed in the textbook. Most textbooks, especially those meant for beginners, simplify rules so that beginners have a manageable framework to work with. They’re not meant to be exhaustive explanations of how a language actually functions. Also, breaking the rules on purpose often (but not always) presupposes an awareness of those rules, at the very least at the subconscious level (aka ‘as a native speaker, I know everyone usually says it this way’), and can be done for a stylistic or humorous effect. What I’m asserting, based on my own experience, is that it can sometimes (or even frequently!) be more expeditious to dive deeper into grammar and studies of usage done by experts than to wait for immersion to bear fruit. Well-written studies and explainers include examples and even exercises that will allow learners to see what the authors are talking about and apply what they have just been taught.
Let me just be clear: I am not claiming that one should study grammar ‘for grammar’s sake’. Japanese textbooks like Tobira list 15 or so grammar points per chapter. I am not saying that anyone should turn those into flashcards containing the explanations given by the textbook and memorise those things. For that matter, some of the grammar points I encountered in Tobira were things I already knew about, and I saw that the explanations in Tobira were completely different from what I already knew and what was in the dictionary (for example, for the difference between the two verbs in the 〜なければならない・いけない structure). What did I do? I ultimately put Tobira’s explanation aside because it seemed that the general consensus was against it, but in all honestly, Tobira’s idea was not in total contradiction with what others had said: it just provided another angle, discussing usage patterns (ならない for one’s own obligations, いけない for someone else’s) instead of semantics (ならない for obvious/natural obligations imposed by external, often societal factors; いけない for obligations that one feels because of inconvenience that could result on a personal level). What I am saying, therefore, is that one should evaluate these things intelligently and use them as an aid for comprehension while remaining mentally flexible. More importantly, one should take note of the language used for describing grammar if one wishes to rapidly find information on precise questions of usage later, even if this is not strictly necessary for learning.
Krashen’s assumption, and yours, is that knowing any sort of rule (which is most likely not going to be absolute, given the nature of language) will constitute a hindrance because real usage doesn’t always match the rules and because it will slow learners down when they attempt to express themselves. My experience is that knowing no rules will leave any learner who is concerned with correctness worried about whether or not they can be understood, for the simple reason that they have no idea what is correct or natural in a particular scenario, especially because their exposure (i.e. immersion) in the language may not have given them sufficient usage examples for them to intuit the rule or at least how something ought to be said. What I’m proposing is not that language can be mastered using a rigid system of rules (which is the usual image we have of grammar), but rather that a balance needs to be struck between the two extremes in order to facilitate learning while preserving the living, breathing nature of language. What I’m also saying is that knowing grammatical ideas can provide you access to the knowledge of those who speak using those ideas, and who are often the very people who spend the most time analysing usage patterns, effectively providing learners with an ‘immersion summary’. That is what I meant when I said grammar is ‘an accelerator’. I’m not saying that immersion becomes unnecessary as a result since an intuitive feel will still need to be gained, but such knowledge can provide learners with handy reference points that will allow them to feel assured that what they are using is close enough to established structures to be understood. This, however, may not be for everyone, particularly when learners have great difficulty with technical vocabulary.
I’m not an expert either, but if you need reasons for why my experience is credible, even if I am aware that not everyone learns the way I do, then here’s a bit about myself: in the video you provided, Professor Brown claimed to speak 6 languages. We don’t know what his threshold for ‘speaking’ is, but we’ve seen that his Arabic might not be all that great since a good chunk of his conversation around 51:30 was about figuring out what day of the week it was. I too have studied 6 languages: I am fluent in three (English, Chinese and French), in which I can write essays, read newspapers and deal with technical topics like politics and science (albeit slightly less so with Chinese because I haven’t used it in that fashion for a while). My Japanese fluency is sufficient for me to read studies on Japanese grammar/usage and websites discussing how to use keigo. I can also understand 60-70% of what’s being said in most of the anime I watch without referring to subtitles. I would say I’m ‘semi-fluent’ in Japanese and rank it right behind my ‘fluent trio’. I’ve been complimented by a native speaker for having ‘excellent German’, but I only have a good grasp of sentence structure and basic grammar. I don’t have much vocabulary due to a lack of practice. The language in which I am the least fluent is Spanish, but thanks to my knowledge of French, I can read newspaper articles in Spanish relatively easily. If you want a specific example of exactly how far my approach and love for technical grammatical knowledge has taken me, then I’d just like to point out that aside from my rather good score on the Diplôme approfondi de langue française C2 (84%, with 45/50 for writing), I am currently studying science and engineering in France, and I regularly outscore my classmates, who are native speakers, in oral assessments for French (between 15/20 and 17/20 for 7 assessments over three years in which I discuss short philosophical/literary essays with the examiner).
In short, this is hardly my first time picking up a new language, and I can attest to the fact that having technical knowledge can be beneficial and is not a hindrance: obsession with correction is a mindset issue, not a knowledge issue, and a perfectionist will fret over possible mistakes regardless of how much or how little he is taught. If you have such knowledge, you can access specialised studies of usage that will give you a good idea of how native speakers speak, essentially giving you exactly the same knowledge you would gain from direct immersion, just that the process would be much slower. However, again, if one dislikes/cannot wrap one’s head around technical knowledge, none of this is strictly necessary for fluency, even if I think it’s still likely that one will have to look up the meaning of a grammatical structure every once in a while, just to facilitate comprehension.