I'll let a shooter do many things. Cheating me out of firing my weapon isn't one of them.
Not that everything should be hitscan. Rockets obviously shouldn't. But any ballistic weapon that takes a fair amount of shots to kill should have a 100% chance of hitting, provided the player's aim is on point.
Skill gap in aiming can be increased by more than making the player lead shots. Just increase movement speed and strafe acceleration.
Good thing every bullet you fire was actually fired on the host box in Halo 3, then. If you had bullets refunded, that means your client fired more than the host actually saw you fire and it corrected your ammo count. The same phenom can be seen if you fire a single bullet out of a BR and melee to cancel firing the last two, you'll lost the last two after a moment because the host saw the melee come in after you finished firing on it's side. Host authoritative is good since it makes client vs client battles much more fair. Client authoritative favors the people closer to host massively and allows more avenues for exploits and modding (you can see how much fun CoD has with modding and it's client-authoritative models..)
Not only that, but both Halo 3 and Reach have bullet magnetism when your reticule is red that means even if you're firing at someone's neck or chest or slightly to the right or left, you'll have the game magnetize your shots towards them and their head. If they upped the movement speed and strafe acceleration then they'd just increase the magnetism to compensate for when the host rewinds to figure out if your shot hit.
Networking: How Does It Work?
There's no reason to keep using idtech 2/3 networking models that were intended for old win95 machines when you have gigaflops at your disposal to actually simulate bullet flight time and trajectory.
Besides the fact that you basically have the overpowered broken starting weapon wet dream, the zero bloom Pistol and DMR.