I’ve never been a big fan of the implementation of dual-wielding in Halo, but the idea is interesting. The problem is that the weapons are useless by themselves. I had the idea that the second gun could be thought of almost like a power weapon or a single-use piece of equipment. Dual-wielding could work if the second weapon couldn’t be reloaded and would be dropped when it was out of ammunition, the player used a grenade or switch weapons. A slight delay in other actions shown with a dropping weapon animation before the next action could help with balance. The player would have a temporary damage increase but be limited in their other abilities.
I always felt it should be always dual wielded, no need to balance combinations, single or dualed. Just have it always be two guns. Right trigger is both guns, left is focus fire. Movement slows slightly, both guns narrow and spread/recoil decreases to offest lack of maneuverability.
Or if they wanted to be cool and lore friendly, left trigger has the guns free aim on two nearest enemies, halfing damage per oerson but allowing you to say jump into the middle of a group and stylishly finish weakened enemies halo legends style.
Or lore wise, left trigger flips the fire selector switch to a spartan only mode that increases fire rate to a higher rate thats harder to control and dumps the mags faster. Possibly only viable at shotgun eac ranges.