The projectile issue actually is much better. Since as a player you're trying to shoot the projectile to "predict" where it will intersect you're actually play

The projectile issue actually is much better. Since as a player you're trying to shoot the projectile to "predict" where it will intersect you're actually playing to the strength of latency and dead reckoning(that's the SubSpace case above). You want to segregate your action into twitch(reactionary: hitscan, parry, etc) and predictive(slow projectile, > 250ms ttl, etc) and only rewind/replay for the twitch case. There's also the case that when you rewind and do confirm a gamestate change you need to gracefully handle resolving it on all clients. That's why you'd see people warp back around corners when shot in Counter-Strike. Their player movement speed slowed after being hit and the server reconciles it and then the clients interpolate the result.