There are two huge problems and they are related: textbooks and entrance exams.
I could never in my dumbest dreams hope to have any influence on entrance exams. That’s a fact. They are a huge problem, because they demand students learn so much grammar and never stop learning and learning more, so they will never have a grasp of the fundamentals. It’s always a race to grasp and translate, but never replicate or utilize, more and more complicated English grammar.
So what is a teacher for? Literally the only point of studying English is to pass an English grammar test that is full of useless and outdated grammar. It’s certainly more than they could be taught in a classroom. A teacher is there to explain how to read the textbook and use the reference book while cramming all night at home.
What is the ALT for? Communication in any form (reading, speaking, writing, listening) is entirely in the hands of an individual student. They won’t learn it in class, and they won’t learn it while cramming, so the most an ALT can do is to encourage students to “like” English, so they will practice using English on their own, apart from their study time.
I could dream instead of writing my own textbook: I would have to study Japanese, integrate into Japanese society, write the book (that’s the easy part), sell it to cram schools and boards of education, and go on talk shows and promote my book to skeptical parents. I really do fantasize about this, just because I wish I could do more to help students. I mean, why in the world can’t someone just fix these dumb textbooks? If it were so easy, someone probably would have done it already. And yet… I think I could do a way better job.