It's interesting that it's latency predictive with corrections and doesn't use anything fancy like operational transformations (OT). I guess it's actually simpler and shared state isn't a collaboratively-edited document but needs an independent, ultimate source of truth, is faster to develop, and probably more performant as a shared server.

Yeah, OT would be way overkill in a FPS, and anyway I don't think OT was even out of the academia in Quake 3's time. And there cannot be any resolution of diverging client states, the server must be the sole source of truth, lest you get cheating and exploits.

OT is dead slow for real time.