Thankfully, no designer would ever hold to such a balancing strategy. You don't balance the game based on a level of mechanical ability that the vast majority of your players are unable to execute.

That is exactly what LoL does. Reread the Morello interview posted yesterday, specifically the section about Elise balancing, and he stats just that.

Champions that are mechanically difficult to use (Elise, Lee Sin, etc), are oppressive by any high tier player that can use them, because their kits, while complicated, have such great synergy not only with themselves, but with the map. This is fine for them to be overwhelming, because only the best players can play them at a level that would be considered overwhelming.

However, it's when they appear all the time, and almost all high-elo players have mastered the basics they need, these champions appear all the time in ranked and soloq, as well as LCS, that they need a change.

Consider Fizz, who held a subpar winrate in soloq, across all elos, being nerfed to his current form. It's not because low elo players were actually able to use him to his best level, it's because high elo players were so dominate on him, that he was almost a guarenteed pick/ban.

They didn't nerf against his subpar winrate in normals or low elo, they nerfed against high elo.

However, when "easy champs" find their way into the meta - champions that even the worst player can pick up and use with a similar level of efficiency as a high elo player can, (think: Ryze, who's most difficult interaction was hover a mouse over the correct person), they become stifling at any level of play. The moment a click and point champion used by a terrible player can shut down the best lee sin without having to think, there's a balance issue - a mechanically dominate player is now able to be crushed by anyone. They nuke said easy champ to allow easier time for our high elo friend.