If these objections that you are raising were wrong, then we would live in a utopia. You're right that people fall short, but I think the point still stands that checks and balances can help overcome human unreliability, even if every human involved is unreliable. Just look at democratic institutions without checks and balances.
I'm actually a big fan of the competing interests concept, it is a very eloquent solution. Where it goes off the rails though is the combination of that concept and the involuntary surrender of individual sovereignty to the very same people with whom your interests compete.
