[immibis]

Reminds me of some of the newer blockchains e.g. I think Binance Smart Chain works like this.

They don't use PoW or PoS. Instead they run on centralized servers like traditional databases. Only, they run on 10 or 20 or 50 centralized servers run by different people and processing the same input and cross-checking each other. Anybody who has money on the chain can stake it to vote for one of the servers (so I guess it is PoS really). Although anyone can connect to the chain and process input, the N servers with the highest stake-votes are the ones that actually count. Also the server owner has to put up some crazy collateral (currently in the realm of $500,000 I think, this is determined by market mechanisms, it used to be lower) and if they are caught cheating they lose it, a process called "slashing". Even having your server go down can cause you to lose some collateral. Conversely you earn collateral while it is up (like in PoS).

So it's really a lot like a traditional database cluster with an enforcement mechanism, and that enforcement mechanism makes all the difference unless your attacker has millions of dollars to waste.