I think there is a limit of the efficiency of a single person. At some point, helping out others to be more efficient is more efficient than doing it all by yourself.

With that said, I don't see anything wrong with stagnating at your peak IC efficiency if that's what makes you happy.

I agree with sibling which says that mentoring is not leadership. Helping out others is not the same as giving them instructions or evaluating performances for example. However I can understand that someone would like none of that.