But in practice, hash power isn't used to choose between forks. Nobody says ETC is invalid because it has fewer hashes than ETH. It's still a valid chain, even though it has less market value. The same would be true of PoS: one fork would have more legitimacy and market value than the other.
If you're not actually forking, but just operating the protocol normally, PoW chooses between branches just fine, but so does PoS. With Ethereum's version, there's even "finality," which means it's impossible to revert more than a few minutes without destroying a third of the total stake: https://ralexstokes.medium.com/the-finality-gadget-2bf608529...
That's a strict improvement over PoW which only offers a probabilistic guarantee. Both systems can be bypassed by a hard fork, but in both cases the fork will face the same challenge of market value and legitimacy.
> Nobody says ETC is invalid because it has fewer hashes than ETH.
I think you are quite wrong there. At some point the exchanges had to pick which chain was going to get the ETH ticker and which chain was going to get the ETC ticker. While it's hard to say exactly why they did what they did, certainly the amount of hashpower on each chain was a significant factor.
If you're not actually forking, but just operating the protocol normally, PoW chooses between branches just fine, but so does PoS. With Ethereum's version, there's even "finality," which means it's impossible to revert more than a few minutes without destroying a third of the total stake: https://ralexstokes.medium.com/the-finality-gadget-2bf608529...
That's a strict improvement over PoW which only offers a probabilistic guarantee. Both systems can be bypassed by a hard fork, but in both cases the fork will face the same challenge of market value and legitimacy.