_act_ summed it up well. It's absurd to compare Bitcoin and Ethereum about decentralization.

They sold premined ETH with ICO. Bitcoin never do that.
Vitalik Buterin is a known figure and have the biggest influence over the market, even for other coins. Bitcoin don't have this type of figure.
They even roll back and forked the coin. Ethereum isn't even in their original chain, Ethereum Classic is.
Switching from PoW to PoS is a hit about decentralization.

Ethereum has its benefits, but it's impossible to talk about decentralized ETH anymore.