Maybe being a senior software engineer also means that you know the difference between what is important and what not in a particular situation. It is very easy to get caught in something that is not really important and put a lot of energy in it.

Another important area is battling with your ego. And this is something, I am afraid, is never going away. You mentioned that a lot of senior software engineers suffer from imposter syndrome. Maybe someone with imposter syndrome is not that senior yet with respect to his battle with his ego.