Capitalism is an extremely broad term. Some specific form of capitalism may well serve the poor well, but it is quite likely that the wealthy elite will not be too keen on that form. And indeed they do typically use the power to skew the system away from such forms. Adam Smith actually wrote about this sort of thing hundreds of years ago.
What it means is they'll trample everyone else, other than their shareholders, to do so.
I wonder if communism could work if the politicians were honest. You'd also need a way to motivate people to innovate in a system where everyone gets the same (except the politicians) regardless of contribution. And they'd also have to do away with one party dictatorships if it is to have a chance.
I think ultimately humans are simply not willing to put in the work and involvement it would take to put communism in place. Neither does it suit those who aspire to power, because there can be no central all-powerful government in a communist society. It's ludicrous to even call countries with such governments communist. Neither is it a system where everyone gets the same. Or one where people could get away with coasting or not contributing.
Capitalism's problem is unchecked greed and communism's is unchecked political power.
That would then not be communism. It's a bit like saying the problem with Christianity is the rampant worship of Satan.
Besides which unchecked political power is a problem in capitalist societies too. Specific checks and balances have to be put in place and constantly, vigorously defended. Nothing whatsoever to do with anything inherent in any sort of capitalism.
Capitalism serves the poor a lot better than the alternatives. The poor still get more wealthy year on year, just not as fast as the folks on top.
In communism the poor just starve to death.
Basically the same as unchecked capitalism then. Additionally capitalism does not guarantee nor inherently do much for the poor. As we can see that allowed to do so capitalism grows the gap and will even eventually increase the rate of that growth by making the majority poorer.