No matter the level of politeness, learning to speak a new language automatically makes you sound like a child at first Pronunciation-wise、ね。
Also, it’s interesting to hear about you actually starting from a speech-focused course instead of the usual grammar-rules /w reading/writing. Pretty cool! I’m guessing you get a different “feel” for the language via speaking it from the start instead of the mechanical grammar cramming. I’ve never heard of people having problems moving from masu/desu to informal forms, but maybe it’s just something people haven’t deemed worthy to mention. Who knows…!
I do agree with others, preferring desu/masu over informal forms as the starting point… and rather than making it a point to call it “polite form”, I’d stick to calling it “neutral” in this case, as it goes with any and all situations.
All the kids in my class would conjugate by starting with ます-form, going back to dictionary form, and then conjugating from there. It was painful. And we still did grammar in the first class, just it was more focused on speaking than writing although we did have writing/reading homework.
When I was suggesting learning casual first, I was more thinking of it being useful in listening situations rather than speaking situations. I do agree that in most speaking situations です／ます would be fine, but again it still depends on the context. The first time I went to Japan I had a short homestay in Okayama and practically the very first thing my homestay family told me was to stop saying わかりません. Although now that I think about it, I’m not sure if it was because of the politeness level or because of the dialect. Because after they said that I tried わからない but they absolutely insisted that I say わかんない.
If you are learning from any language textbook-you will be taught the standard usage and structure of that language. It doesn’t matter what language ( at least I don’t think so). Textbooks are set up to teach you the foundation for a language. In English it is the same way. In school you are not taught slang or the way that people speak to each other socially or the differences in dialects. I would guess that Japanese children are taught standard Japanese in school too. The casual stuff comes with living and growing up in a culture.You learn when and to “use” your native language in different settings Plus a lot of people learn Japanese for positions where it is important that they speak properly. Anyway, that’s just my little opinion. Here is an article that talks a little about this: italki - Basics Of Informal Japanese Speech and tofugu has this Keigo: The Importance of Politness in Japanese
Haha, sounds like you had a chill homestay family! Not 100% certain if 分かんない belongs to any dialect - at least it’s used throughout Kansai along with 分かれへん. In any case, I see where you’re going with the casual first -suggestion, especially considering your homestay experiences, with which it makes a lot of sense. But as @justjanice said, desu/masu remains to be the foundation of the language etc.
I quite like the textbooks teaching desu/masu and other polite forms first as you do get plenty of exposure to the colloquial language if you spend even a short period in Japan / have local friends. I know I got so used to colloquial, that I’m worse off when it comes to trying to remain polite. Always slipping back to “えー、そうなんや！！” when I’m supposed to stay with そうなんですかー and the likes.
Pronunciation-wise、ね。