First I’ve heard of Arcane. Is it actually good and worth watching if I have zero interest and know nothing about Lol, or is it really just rated highly because of anime/gaming fans?
It's among the best quality animation I've seen. Story is excellent in the beginning, though degrades to only decent towards the end as the video-game origins start showing through. Definitely worth watching, IMO.
(I also have no knowledge or interest in LoL.)
I've never played league and don't like most anime, just found the show and thought it was amazing.
The ideas aren't anything new but the execution is pretty good. Overall, a solid 8/10 I think.
If you enjoy animated shows, you don't need to enjoy league.