I disagree. though my English is still not perfect, everything I know I learnt through immersion (mainly on reddit), and it didn't take very long. when I started using reddit, about 1 year and some months ago, I could barely form proper sentences and only knew basic words such as "cat" "dog" and "car". less than one year in, I was able to have long conversations and discussions, and shortly after that I didn't even need to look up words anymore. all that without ever having to learn a single bit of grammar and conjugation rules. everything just came naturally. now I'm comfortable with writing and speaking, and I'm able to read giant books in english without any kind of trouble.