I like to think about it by comparing it to where I’m at with English (my native language). I’m a fairly proficient reader who can read academic texts in the disciplines I have expertise in, but I’d struggle reading scholarship for STEM fields I have only limited experience in. When I mentioned to one friend that I was using Anki for Japanese, they were surprised, haha, because the only people they knew who used it were people in medical school. They’d never considered using it for language learning, though I think effectively those students are doing the same thing, just really high level language learning.
So, I think depending on your goals, there’s never really a true “end” to SRS. You can always learn more and more advanced/specialized vocabulary if you choose to pursue that. I’ve gotten so used to SRS reviews with Japanese, I’ve had moments where I forgot a word in English, looked it up in the dictionary, then had the “I should add this to Anki” thought. And, yeah, I could create an Anki deck to improve my English as well, if I wanted. There are all sorts of words I’ve learned but forgotten, and I’m constantly learning new words.
Even outside of academic disciplines, loads of everyday things have their own specialized vocabulary. Getting into pro wrestling has forced me to learn all sorts of new terminology, like heel, face, work, shoot, kayfabe, selling, gigging, hardway, getting over, going over, jobbing, heat, pop, mark, apron, bump, cutting a promo, etc., and that’s not even counting move names! Could I have learned all this faster by feeding a bunch of terms into Anki and drilling it? Absolutely. It would have taken me much less time to learn, and I would’ve had fewer occasions of accidentally using the wrong jargon or having to ask my friends to define terms for me, haha.
I think it just comes down to your own comfort level with where you’re at in the language. If you aren’t satisfied with your vocabulary and want to learn more words, SRS is probably the most efficient way to do that, but that doesn’t mean it’s the best method. I think picking up wrestling terminology naturally over time was fine for me, but if I was in medical school, I’d go with SRS. Efficiency would win out for me in that case.
With English, I’m at a point where I’m happy with just looking things up in a dictionary as needed. If my Japanese ever reaches that point, I’ll probably stop SRS-ing things, because even though I don’t really mind SRS, if it’s a choice between using my time to read for fun or for studying, I’d rather read. But at the stage I’m at now, SRS makes reading substantially easier, so I’d rather do some SRS with a little less reading, instead of doing more reading that is more difficult for longer.
But there are plenty of people who learned without ever using SRS, or people who use SRS for only a limited time and then drop it and learn without it. At some point, efficiency stops mattering. You’ll forget more without SRS, but forgetting things is kind of inevitable. You just have to decide if remembering as much as possible is more important to you, or if you’d rather use your time to read more and spend a little more time with a dictionary.
I don’t use Migaku, but their reasoning for retiring your flash cards makes a lot of sense to me, so I have an Anki extension installed that does the same thing. Maybe I’ll change my mind on this in the future, haha, but I think I’m happier with using SRS for the first stage of learning a word, then letting exposure and/or a dictionary take care of it beyond that point.