It says nothing about whether it's optimal or not. You can't easily evaluate how good a UI is for expert users until you're an expert yourself, and once you've made that effort, will you really want to abandon all that hard-won skill to learn another system? I think many people use sub-optimal UIs because the short-term cost of learning a different one, which might not even be better, is too high.

True, and that includes me. My favorite thing to say about bad UI is "those designers should spend two weeks using a Mac from 1985". :)