Also let us not forget other tools that have significantly helped capitalist nations: Slavery, Colonialism, Imperialism, Sanctions, Wars, Coup d'etat's... these have all contributed to what capitalism is today. So yes Capitalism in the grand scheme of things is entirely zero sum.
Once we reach the end of the road for further invention and improvements (even if that is in the form of our own capacity and theoretically there's more), that's when capitalism becomes zero sum. Until than point, capitalism is a way of distributing more resources to people who are better at finding those improvements.
The entire foundational assumption of (Smith's) capitalism is the idea that people who are better at making a profit are exactly who should be given more money to work with, and that this benefits all of society — and while I will agree that the phrase "trickle down economics" doesn't fit reality of the behaviour of billionaires (who act more like aristocrats), that's where that phrase comes from, and it seems to often work up to deca-millionaires at least.
The flaw with this (even in the case of millionaires) is it presumes no parasites. As it happens, both Smith and Marx noticed this, but as history shows, the proponents extolling the virtues of each were not very effective at preventing economic parasites.
