There is no bright line difference between proof of stake and any other type of consensus, committee or voting body. Proof of work of course is very different.

The difference is enormous: in one case, you don't need any centralized N entities, just a big percentage of the network, whoever wants to participate, runs the protocol and there are no 50 institutions / companies that can block it without reaching the majority of work / stake. In the other case, you are delegating the consensus to a fixed amount of parties. Now, we against the crypto / blockchain shitstorm advertised the alternative of old-style federated consensus with N trusted organizations for years and years. And now, no: you can't say, this is a form of blockchain. You admit failure and acknowledge that classical consensus was good enough and even better in most cases.