Political Memes

a huge monster that no longer innovates and instead continually enshittifies and becomes an overall parasite on society that blocks competition and stifles innovation, often capturing regulatory agencies and doing all sorts of unethical things with no consequences.

Regulation that prevents the anti-competitive etc. behaviors directly, instead of trying to assess a roundabout 'fine' based on net worth (which also carries the implicit assumption that any entity that reaches the 'cap' does so unethically, which is absolutely not the case—for example, Costco is a company with a famous reputation for being generous to both its customer base and its workforce, and it's valued at several hundred billion, its founder is a billionaire himself), is the best way to approach this, I think.

And honestly, if we're at a point where the sources of the regulation are truly "captured", then we're also at a point where trying to deal with the above behaviors with a tax is even less likely to succeed. Fixing that 'capture' should be the primary focus in that case.

At that point, the company and the individuals controlling it are no longer net contributors to society and need to be put in check, or otherwise, it does become a zero-sum game.

That's not really what "zero-sum" means. What you're describing is the company/entity becoming a net drain on the economy, but that doesn't change the fact that wealth isn't zero-sum. Being zero-sum would mean that it's impossible for the grand total combined wealth among everyone to ever change, and therefore no one's wealth can ever go up without someone else's going down, or vice versa.