In order to compare the most popular PoW pools with the most popular PoS pools. it would be like giving your miner to a 3rd party and having them do all the work. In that case they would practically own the equipment and you would have a hard time switching to another pool in case of emergency. In ETH they believe its not a problem, maybe its not, as long as Bitcoin exists it will keep ETH more honest and fair, regardless of how much it centralizes. But if ETH gains a monopoly, it will show its true face.