They need to go back to the way Halo Reach Progression system worked its a fan Favourite and could revive Halo.
The feel when you would grind to level up and get new Gear made the game worth grinding.
Keep your REQ packs for Warzone and getting Camos for your weapons but make the level system for unlocking armour and general Ranking up the same as Halo Reach was. The Levels were all very interesting unlike Halo 5 very boring level system.