“As has been true for the last seven years, no more than five mining pools control the majority of the Bitcoin mining power and last November two pools controlled the majority of Ethereum mining.”
Rosenthal co-wrote a proof-of-work consensus paper five years before Bitcoin existed. His verdict on the result is that decentralization lasted about as long as it took miners to form pools. Two pools ran most of Ethereum. A system that needs no trusted party now runs on trust in a handful of them.