That’s where it gets confused. In D1 there was primary, special, and heavy weapons. They took those individual ammo types, and all had elemental types except kinetic weapons. All kinetic weapons used primary ammo, including exotics such as NLB and Uni. Elemental primaries used primary ammo. Now with D2, its been mixed up a little to be the kinetic, energy, and heavy slot. Individual weapons can take primary or special ammo yet be in the kinetic or energy slot. The big draw of Supercell was that it made your primary into an Arc type, so in D2 it would be in the kinetic slot. If they put it in the energy slot it just wouldn’t be as valuable as it was. Then there was Adept Raid Weapons and the like, that all replaced the first slot on your character with an elemental weapon. I’m saying that that is something that Bungie seems averse to doing again.