So... Most games ignore modern hardware capabilities in order to support a fragile programming model? That doesn't sound like an argument against my point. My point was that mutation makes it harder to get code correct. If the only way you can do it is by refusing to use more than one thread of execution for calculating game state updates, that's not evidence that there's no problem with that approach.

Of course, this does vary heavily by game. There certainly are games that run their world simulation across multiple threads. https://twitter.com/axelgneiting/status/1241487918046347264 is a pretty awesome note about that in the Doom Eternal engine, for instance. But I'm certain getting that to work required very carefully controlling when and how mutation happens.