TrathBalance will always be imperfect. Heros are changed to be stronger/weaker every patch. I would imagine its the same for Dota?
There's a balance patch for DotA like (at the quickest) maybe once every 3-4 months. Nowadays, new heroes come every 6 months-ish (in DotA 1 anyways since then they're actually new)
Icefrog actually lets people adapt and find new strategies, but then again the heroes in DotA are actually complex and nuanced enough that the metagame shifts like crazy regardless of balance.
League heroes on the other hand aren't complex (partially because you have to buy them so no one owns them all really, partially because Riot has the most retarded design ethos ever "xd you should know what a champion does instantly instead of have to learn anything") which makes the ban/pick process in LoL just really dumb, the gameplay gets more repetitive faster, and none of the heroes are really THAT interesting in comparison.
It's not even like I'm just a biased fanboy or something, I actually play both quite often, but Riot is a scummy company as far as e-sports go and most of their backend/cash shop is horrendous. The champion design is just icing on the cake.