It doesn't really matter what the system of government is, power-hungry psychopaths will always attempt to game the system in their favour. The history of governance is just a long arms race of inventing new systems to thwart them while they do everything they can to corrupt those systems and concentrate power in themselves. It's like fending off griefers in an online game, there's an endless supply of them, they don't care about the rules or the game, they just want to dominate other players for their own perverse enjoyment. The only lasting solution would either be some form of genetic modification to remove that trait from humanity entirely or some perfect way to identify them but you'd have to be extremely careful that they didn't gain access to and corrupt those things before they were completely eliminated.