I'd argue that if you don't focus your efforts on the things that really matter to you you're going to have a tough time transcending mediocrity for entirely different reasons.

If you avoid all activities and requirements that you don't enjoy then yes, you're going to have a very hard time becoming good at anything. But if you take on every challenge that you can just because it's there, you're going to fail at most of them and have a much harder time with those you really do care about.