This account could be an interesting case study for the comprehensible input hypothesis of language acquisition. Narrowing the language domain and pre-studying vocabulary may have helped the effectiveness of the study: https://en.wikipedia.org/wiki/Input_hypothesis
The Japanese learning community has wholesale adopted the Krashen school of thought, tons of us learn almost exclusively by comprehensible input, myself included. I spent about 50 or so hours on grammar at the start, a list of 1,500 words and the rest has been purely reading and watching what I want and playing video games. At about 1000 hours total since last June I'm able to read a lot of everyday Japanese without much difficulty. I plan on taking N2 at the end of the year.