As for decentralization I seriously see this ETF of a thing just like the centralized exchanges they are there for people who do not value decentralization but does that affects bitcoin as a whole I will say No because bitcoin is pseudonymous and can be used by any in anyway they deem fit. The only time I will worry about decentralization is when there is censorship in node running or miners censoring transactions.
After doing some research on ETFs now, I can comfortably say that they are just as centralized as CEXs since the coins aren't held by the individuals themselves, and they only buy shares from the ETF companies themselves and rely on the companies for safe keeping on their bitcoin. These people do not take decentralization seriously and left their coins in the hands of a third party.
I see now the reason government approved 11 ETFs last year since they are still propagating the gospel of centralization which is the government's love so much.