I think the claim is that capitalism increases (something like) total wealth but this does not necessarily entail increasing the wealth of each personal individually. In fact, most people could see their wealth decrease under capitalism, and some such as Piketty would (I think) say that this is the limit we are heading towards.

While I agree that capitalism is responsible for quite a few good things, at the end of the day it's just an (extremely stable) economic system, and figuring out realistic ways to deal with some of its shortcomings seems like an incredibly important problem, though not one I know how to solve.