Halo 5 was onto something with Weapon Variants in a way. While I hope Variants never return in a gameplay-altering way, I hope they make a comeback as purely cosmetic skins. Customizing the look of your gun not just with a simple paint job, but with a substantial visual change, would bring a lot more variety without mudding the sandbox.
I say: when 343 keeps the selection of arms small, but expands ways to change looks we get the best of both worlds.