There's only like 2 things they'd be able to do with a majority hashrate, and even then their success is unlikely. They could censor transactions, which would still get through eventually, as those transactions are mined by other pools. This would be publicly visible activity on sites like miningpool.observer and would be called out. Then they could also do a 51% attack, which would also be publicly visible. I think the risk with the 51% attack is the scenario where they rewrite the chain any time an honest miner includes a censored transaction.

The problem with this is that as soon as such malicious activity is reported publicly, we can safely assume that both of these mining pools will lose a significant amount of hashrate. Meaning they practically only have one shot to censor some transactions until hashrate is pointed elsewhere. Then what? They'd lose all (or at least a majority of) future mining profits, and no one would realistically use them again.

Bitcoin would benefit because it would demonstrate how meaningless this type of attack truly is and it would likely accelerate R&D in mining pool tech. It might also show how shit KYC and get more people on-board with avoiding all forms of KYC when it comes to using Bitcoin. So yeah, IMO, this is just an old argument that's been "hashed out" over and over, and is a total nothingburger.