There is lots of evidence that people in power are the most rational, but there is a huger prior to overcome.

Among people for whom power has an unsatiated major instrumental or intrinsic value, the most rational tend to have more power- but I don't think that very rational people are common and I think that they are less likely to want more power than they have.

Particularly since the previous generation of power-holders used different factors when they selected their successors.