You're claiming that if capitalism tends to backslide into X, then X is part of capitalism. My point is that every system can backslide into something more primitive where a strong man makes the rules. They're not all the same, so your idea that X is an inevitable part of capitalism is wrong. Capitalism is what we call it when it has a certain set of characteristics. If it no longer has those characteristics it's no longer capitalism.
I’m claiming that capitalism in particular is one of the most corruptible systems
And you're wrong. There's nothing about capitalism that makes it more corruptible than feudalism or oligarchy. In fact, those systems are much more corrupt in general.
It tries to harness the power of greed and turn it into positive sum games
Whereas feudalism doesn't even try to do that. It just skips the positive sum games part and accepts greed. At least with capitalism there's an attempt to make things better.
I think greed driving society maximizes corruption
Maximizes corruption? You think capitalism is more corrupt than a strong man system where everybody is forced to constantly flatter and pay tribute to the strong man? A system where the rules are whatever the strong man says, so bribery is baked into everything?
think we should replace that with something else
Sure, let's do it, what do you propose? And how do we get there from here?