From my experience, in general, the very brightest minds (of those who have zitzfleish) do stay in Klei Kodeish. However those a little less than the very best feel they are too smart to teach elementary school and if they aren’t going to be a rosh yeshivah or rosh kollel they may as well not take tuition breaks and become lawyers, doctors, entrepreneurs etc.
The reality is that there are very few Rosh Yeshiva/Rosh Kollel positions and fewer still where you don’t need to have a close family connection.