Dota has less problems with this because the meta played on the map has been allowed to change wildly throughout the years, while Riot have mostly been trying to enforce one single meta (last I checked anyway, which was a long time ago)

If the game only has one map and the characters are bad on it, isn't that a character design issue? You can change the map to be more varied/balanced, if it's restricting the design that much. Adding more maps won't make the first one more fair. That's just rock paper scissors. And that's fine for a small, casual game. But league wants to be a skill based competitive game.

Yes, the map has evolved. They're trying to make it more varied and more balanced. But there's still only one map. Which is what league is probably going to do, because it's better for the health of the game. Adding more maps doesn't solve any design issues. It just makes balancing even harder.