heyy, have you read One Piece?
It's the leftiest, most anti-imperialist anime/manga I've seen to date. Although it has cartoon-like art, the themes are serious and deeply political.
Also most people have issues with it being too long... the problem is quite the opposite the more you read/watch, it's actually too short for how many well interconnected mysteries, characters and places there actually are, everything is fleshed out.
Also it doesn't get worse with time like most long series, it gets even better!
Good luck on your Sails if you haven't checked it out yet!
Oda is a secret propagandist, who got to make the most popular anime in history, truly a madman genius if you ask me