Consensus on which rules to use happens on a different level. I'd say that it's economic consensus enforced by network participants. There's economic incentive to use rules which will not split the network.
That means you can't tell what the correct chain is just by counting hashes. You have to ask someone what the currently correct software is, and then you can find the correct chain for that software.
This puts you in the same position as someone on a proof-of-stake chain.
This is completely different issue than chain consensus disputes, which means that inside the chosen rules there's disputes on which history is correct. I.e. it's the double-spend problem, which PoW solves. PoS is subjective, and it's impossible to determine the correct history without asking someone. [0]
[0] https://hugonguyen.medium.com/proof-of-stake-the-wrong-engin...
In this sense there could only be Bitcoin. PoS cannot come close to that at all.
P.S. To clarify a bit more - I don't think the most-difficult chain can be with broken nonsensical rules, not in the long term.
Compared to Bitcoin as it exists in the real world, PoS has advantages.
You assume that the community somehow can agree which chain is the correct one in proof-of-stake. This is not true because there's no longest chain rule. Without an authority, users would never be able to converge into the same chain, after a split has happened.