I wouldn't say that Ethereum is fully decentralized. Only partially perhaps. There is this developer team with an uknown premined stash, who decides what to do with the bloockchain. This is done without asking the users, including reversing transactions in case they don't like something. This is what happened in 2016, after the DAO accident. Since then the project has been compromised and nobody can state that it is truly decentralized.
It is a fact and an important part of Ethereum history from that people have evidence to say Ethereum is centralized, partially even the project and the network have changed a lot in many years after the DAO hack.
Now we see a switch from POW, which was the only decentralized element, to a POS, which is like the fiat money. So with time instead of going more decentralized, ethereum is going even less decentralized.
The power will be centralized in hands of big exchanges. They will hold the most Ethereum on the network and it won't be good for Ethereum network. Exchanges are targets of governments and have more centralization on exchanges means more risk for Ethereum network.
This is one of the reasons many people,,, including myself, changed their minds about Ethereum. Even Vitalik himself admitted at some point it was not as decentralized as he would like and took steps to changing that. The fact that dev calls take forever and decisions are "slow" show that the method eventually works.
He tries but it does not mean his vision can work.
BSC can also achieve that I suppose but not for a long time yet.
BSC is worse than Ethereum network because that chain has very little validators and they are fully controlled by Binance. Binance again are one of most favorite targets of governments now and in future. It means that chain has already been under radars for more regulations then FUD.