Centralization remains an issue
That's why PoW provides a 51% mechanism.
It works both ways, any 51% attack can be 51% attacked.
Don't make me laugh. You think you can 51% the government? lol
That's why we have an anarchy of competing governments.
Governments aren't going to be 51% attacking each other to protect BTC users' autonomy. The majority of governments work in concert with each other. "Competing governments" are an illusion.
... unless governments themselves become BTC users, which they should.
It's a good question though. In the scenario of a single totalitarian world government PoW might not be the best option and instead a myriad of anonymous PoS coins will serve better. Though it would not be a perfect global money system for variety of reasons. This solution is temporary and so is the one world government. Once it falls apart PoW provides a neutral playground for competition.
We are far from the scenario described above, because there are clearly big countries who agreed to disagree. We need both systems as each serves its own purpose, so we will see how this plays out.