It’s a problem of psychology and scale. The communist system becomes susceptible to bad actors the larger the group becomes.

How? What makes it more susceptible in ways that Capitalism is better?

In point of fact: I fully agree that many Latin countries, absent US bullshittery, intervention, and fomenting of coups in the first Cold War, would probably mostly have wound up being successful.

Cuba is doing pretty well despite the brutal embargo.

But I absolutely do not agree that the USSR or the PRC should be held up as paragons of virtue of what a Communist system should be. They were very quickly corrupted by authoritarian leaders and cliques from the get go, which is genuinely antithetical to true communism.

No, they were not. This is vibes-based analysis mixed with Red-Scare propaganda. The USSR and the PRC were both Socialist (and the PRC remains so to this day). What do you mean by them being “quickly corrupted by authoritarian leaders?” You mean that they elected the wrong leaders in your eyes, that they should have gone against democracy?

Inequality shot far down in the USSR, and the Working Class was in control. That was absolutely Communism in action, regardless of your vibes-based analysis. Obviously many things also went wrong, they all had their struggles, but they were actually existing Socialism and should be analyzed as such.

I highly suggest reading Blackshirts and Reds.