I have to tighten your earlier point a bit first: it is not just absolute concentration of wealth that causes this, it is high levels of inequality, e.g. lots of people in misery with a few folks that have ridiculous riches.

I'm pretty sure the commoners (and even more so, the slaves!) in Rome, Egypt or Imperial China didn't love the system either.

However, I think the average modern-day, communist Chinese person has seen such a rise in standards of living (one billion people pulled out from poverty!) that they don't really hate the system despite there also being high wealth concentration amongst party and business elites.

The gap is the problem, not the peak.