Cartels, monopoly, and regulatory capture are inherent to the human condition.
Either way, it's not really the point whether it's inherent to human condition. It's obviously a failure mode that can happen in lots of circumstances. I think the difference is that in capitalism it's highly incentivized by economics and culture and capitalism as a system doesn't have many great defenses against it. Anti trust legislation is as you pointed out vulnerable to regulatory capture.
I think capitalism stans would have more credibility if they would acknowledge that any complex system for distributing resources will obviously have edge cases and failure modes that need to be addressed. Denying that anything is the system's fault again just sounds like the "that wasn't _true_ communism" people