GPU or ASIC...it makes no difference once the farms start mining. In Ethereum it only takes 3 of the major pools to make decisions on a specific fork for the entire network.
Bitcoin is same.
It's not the same. Bitcoin's blockchain is owned by China ASIC manufacturers. ETH PoW is available to anyone and uses off the shelf hardware. As long as it stays that way ETH will be as close to decentralization as it gets.
Ethereum mining is more decentralised than the bitcoin mining. But it will gradually centralise in cheap energy places.