Don't understand why some Ethereum critics say Ethereum is centralized as they can just change their monetary policy whenever

I don't understand why some Ethereum critics say Ethereum is centralized as they can just change their monetary policy whenever.

They still need nodes to support their decisions so it's still decentralized. Vitalik or whoever cannot just change whatever willy nilly, the nodes still need to agree. Switching to proof of stake was also the only logical answer for Ethereum as it would not have survived for its purpose if it did not. As if Bitcoin is any different. The developers at blockstream basically got to choose what to add to Bitcoin core anyways (such as keeping block size small).