> The security model of Bitcoin comes from proof of work

This is not the security model, this is the consensus model. It's based on probabilistic finality, meaning that the probability that a transaction won't be reversed increases as more blocks are added on top. One major advantage of PoS is that it has "Absolute Finality" - after a certain amount of blocks, it's absolutely impossible to do a 51% attack. (See https://medium.com/mechanism-labs/finality-in-blockchain-con...)

Note that a higher hashrate does not mean more secure, it's a common falsehood. The security of bitcoin depends on the percentage of miners that are honest - this is mentioned the bitcoin whitepaper. Fortunately, the incentives align for the majority of miners to stay honest, and this is what the whitepaper predicted.