> capitalism is a zero sum game, thus the disincentive to give what you've got.

Only in a zero growth environment. And in one, which economic or political system is not a zero sum game?

> consider that our planet is fucked by global warming thanks to "optimal resource allocation" which takes no account for long-term consequences

Pricing in long-term consequences and accounting for externalities is arguably not a contradiction to capitalism (and I think we should absolutely do much better there).

Ideally we’d even account for the effects of societal unrest due to massive wealth inequalities or areas becoming unlivable due to the climate, or just the immorality of poverty if nothing else.

But that’s a political decision (what do we value how much) in the end, not one of economic systems. Who gets to decide that is determined by the political system, not the economic one. And corruption of political power can exist in all systems.