So what I think is a really strong counterpoint to your argument is the simple fact that watching movies in a language is generally considered a great way to learn said language. That's passive learning in a similar manner to what you would get out of reading in a video game.
It fails to train you in actually synthesizing speech though. So you need a structured approach as well, similar to what you describe, to fill out the many other facets of learning.
But it's still insanely valuable to do so.
reading things likely makes you better at reading things
Well, I think doing things way above your level "works" sometimes in the sense that there's a subset of things that a learner happens to be most receptive to at any given time, and immersing yourself at the deep end is a bit like brute forcing through the entire subject matter until something happens to stick. But this is inefficient and not guaranteed to yield any results at all.
I have some insight into language learning myself, having had both positive and non-positive experiences. On the one hand, yes, games and movies did help me pick up english vocabulary, but this is because I also studied english from an early age in school, the fact that English borrows vocabulary heavily from romance languages (with which I am fluent), and perhaps most importantly, the fact that I've immersed myself in it quite deeply during my teens, often preferring to read and write in english. Ironically, though, learning through entertainment media left me with some curiously weird learning gaps. For example, I only learned in my 30s that "down" (as in Final Fantasy's "Phoenix down") refers to a type of plumage and not some weird in-universe usage of up/down/left/right.
Now contrast this experience with this: As a kid, I also learned Japanese (though not to the same extent as english, let alone the extent required to master it coming from a romance language). At one point, my dad brought over some Japanese RPG games from a business trip to Japan, and while I did have basic schooling on hiragana/katakana, the teen-level kanji from the games was way over my head at the time, and I ended up learning virtually no Japanese from those games (I had to quite literally sit down to actively study kanjis to make any sense of what the game text said). I also consumed quite a bit of anime and not a whole lot stuck with me either, due to a lack of what I can "active practice" (i.e. my exposure to the language was mostly on a as-needed consumption basis, with little to no active effort to write or speak).
In short, I do think games can help nail down stuff you've learned elsewhere, but upleveling language skills from games alone is very difficult.
> For example, I only learned in my 30s that "down" (as in Final Fantasy's "Phoenix down") refers to a type of plumage
For what it's worth, that's not at all what I'd consider a weird gap. As an educated 40-year-old native English speaker, I think it's possible I've gone my entire life without speaking aloud the word "down" in the sense of plumage. I'd only expect a non-native speaker to know it if they spent some time focusing on animal terminology.
Yeah, after writing that comment I thought about it a bit more and realized that I have used the word "down" in the context of pillows before. But that may have been one or two conversations in my life.
It fails to train you in actually synthesizing speech though. So you need a structured approach as well, similar to what you describe, to fill out the many other facets of learning.
But it's still insanely valuable to do so.
reading things likely makes you better at reading things