It does cap the wildest, antisocial forms of success that are insane excess.

Progressive taxation should mean you can never gain enough power, which capital is, to warp your society with power beyond your single vote, whether that power is expressed through direct bribery, lobbying, or mass media propaganda to try to trick your fellow citizens into voting and advocating against their own interests with your booming, capital powered voice that drowns out those you disagree with merely because you've exploited more capital into your private account than others.

I don't see any shame, horror, or problem with putting a hard cap on how much an individual can accumulate, as other people live here too.

Despite what Elon Musk believes, this whole planet shouldn't be his personal playground, but that's what it means to become a trillionaire, entire governments will bow at your feet. That's perverse. No unelected, unaccountable individual should hold so much power, unless humanity wants to live in a hell of its own making.