Wouldn’t call myself a polyglot but for Japanese I learnt mainly through absorption, with one-on one classes to grasp the grammar (which I can’t say I’ve exactly grasped lol).
I learnt some Cantonese and Mandarin through in-person classes and watching a lot of movies but without being surrounded by it it just leaks out of my brain.
So basically I think it depends on the person. I know some people who only took classes in Japanese back in the UK and ended up exceptionally good at doing the written exam and can read books and academic articles but can’t order in a restaurant as nobody can understand their pronunciation.