In my studying (no, acquiring) Japanese I notice a huge difference when I can do 1.5 hours (or more) a day instead of 20-30 minutes. It's almost like the latter is useless. (Edit: The latter is more than enough to learn grammar etc. But that doesn't teach you the language, unlike what they believed in school way back then)

That may indeed be true. Plus exposure - as kid I had that. Now Duolingo and what not…not the same