My English classes, grades three through twelve, were always "here is a book. Now write a 10 page essay on how the author's description of the cracked road surface is a metaphor for the moral decay of society" - i.e. modern artist training class.Respectfully, your experience is limited to school.
I can already tell you its paying off for you. Even if all they did was make you read for 2 hours straight, that's good enough. Unless you're brutally leaning on your auto-correct, your English and grammar are excellent.
Its not about learning new words, its about ingraining language itself as a tool. It makes it easier for you to vary your vocabulary to a specific task, understand others, and frankly make yourself look smart.