That might still leave many people poorer than under capitalism.
Nope. The promise of communism is the satisfaction of all your needs, not just satisfaction of what we can afford to, given the limited amount of stuff/services which we have available. It is supposed to be a place of plenty, not just a place where thin gruel is shared fairly.
I suppose you can, if you want, define "communism" so narrowly that nothing counts as communism unless it brings about an early paradise of perfect plenty. To me, that seems much too narrow a definition.
Imagine that someone tells Karl Marx that the economic system he advocates will not bring about a permanent end to all kinds of want. Which is the more likely response, supposing he believes them (of at least is willing, arguendo, to stipulate that they're right)? "Oh, then it turns out that what I've been advocating isn't communism after all" or "Oh, then it turns out that communism doesn't work as well as I hoped"?
How much money would it take to engineer biological immortality for at least half of the world's population, within 20 years, with 99% confidence?