I’ve played EVEN MORE Halo: Reach and I’ve almost completed the entire Campaign on Legendary. It is amazing. The Pillar of Autumn mission is cheating. Grunts are OP. In just a couple shots on legendary, they will kill you. It’s totally unfair. I have discovered the best way to kill elites.
All you have to do is shoot it with a charged plasma pistol, then shoot it with a DMR. That makes life easier. In my opinion, the plasma pistol is the best weapon to use. Shooting it rapidly at brutes or brute chieftains will kill them. The best weapon combo (in my opinion for campaign) is plasma pistol + DMR. For multiplayer, use anything you can find, because other people usually get it first.