While meritocracy in high dimensional humans is a muddy thing, as being capable, and being capable at what is actually needed often diverge.
But at the organization level, the benefits of strong coordination of the right things are clear. Virtually every business study, studies this. Virtually every political leadership study, studies this.
Cooperation has so many efficiency and effectiveness benefits. Institutionalizing the right kinds of cooperation, i.e. coordinating it, even more so.
This is the civilization superpower.
This is why billions of people can spend their days doing other things than food production, and can live in places with no food production in sight.
But being really intelligent, at least for the top 1% or so, is often advantageous enough to offset any disadvantages from your class/cultural background etc.
I also wonder whether your "psychopathy" is just "ambition". After all, while intelligence alone doesn't guarantee anything, "intelligence + ambition" takes you quite far.
Personally, I can see how even an honest-to-god meritocratic society ends up with psychopaths at the top. For most people with normal-ish psychology, the risks and stress that comes with being on top of anything high stakes is just too much.