And then there is the whole issue of keeping morale high among the producers when they get paid the same as the guy who does just enough to keep out of the gulag. For these reasons, Communism could only ever work in a society of robots.

Productivity isn't just 10% or 20% more. In some industries (like software), the top producers can be 10x or 100x better. Even in a grocery store, look around, the top checkout clerks are 50% or 100% better.