Some blockchains are more centralized than others. There is a danger that Ethereum could be subject to a takeover now that it's moved to the PoS model. The majority stake of ETH (and power to govern it) is actually in the hands of a few of the largest exchanges now and thus it is already very centralized.

That's happened because people are stupid, and store/stake their ETH on exchanges instead of setting up their own nodes. This means they don't really own those ETH, the exchanges do. ("Not your keys, not your crypto.")