There was a point made that 4 groups of mining pools can perform a 51% attack if they were orchestrated. That's not really decentralization is it if such a thing is possible already?
Nodes control consensus in bitcoin. If miners attempt to circumvent the will of the users, the Proof-of-work algorithm can be changed, making useless all of the miner hardware. They know this, which is why they can't force the issue.
Decentralization of mining is an issue, but decentralization of nodes is a far more important thing to maintain.
People often make observations like this, about lots of things. "It's not 100% perfect so what's the point?".
The point is it's closer to 100% perfect than any other system we have. Incremental improvements are still improvements even if they aren't all things to all men.
Decentralisation isn't black and white, it's all relative. Bitcoin is more decentralised than fiat currencies and traditional banking. Isn't that obvious?
