>> Those that will do anything for power have an advantage over others, ergo people at high level positions are disproportionately those types of people.
One thought is that we could try to fix that problem with some type of screening, but that would be another system to game or corrupt. Also, those kind of people (high ambition and drive) can be really useful in those positions so long as they don't go off the rails.
I like the solution from Hitchhiker's Guide to the Galaxy: Elect some random person as president of the galaxy, but don't tell him about it. Just have conversations with him to find out what he thinks about things, but don't let him know that you actually run the galaxy based on these conversations. If power corrupts, make it impossible to seek power, and don't let the person that wields it know that they have it.
This is pretty much how the Shogunate in Japan worked.
Once a single war lord controls the “security” of the Emperor, they then wield power and justify all of there actions based on sole access to the Emperor.
One thought is that we could try to fix that problem with some type of screening, but that would be another system to game or corrupt. Also, those kind of people (high ambition and drive) can be really useful in those positions so long as they don't go off the rails.