So USSR was a dictatorship, the country was in ruin after WW2
The 3 factor i mentioned are there.
The data shows what everyone knows, capitalism increase inequality. But what it doesn't show is how communism made the country improve, because it didn't.
What i'm saying is, it couldn't help because of the war and Stalin. We don't know if it would've otherwise.
Cuba again is a dictatorship, and wasn't rich.
The PRC is a dictatorship, China went on a horrible famine with Mao. Nowadays getting richer only because of how their economy is now fully capitalist.
So let's say you had significant data that showed it improved some things socially. And let say you somehow managed to prove its causal and not coincidence.
I would still rather not say dictatorships like USSR or PRC are good to live under.
That's my point, even if communism was good, dictatorship is a plague that makes any system a nightmare.