setslot is actually a prewritten console command, meaning it gets run last of all at load. Because of this, it will forcibly overwrite any other methods of setting weapon slots, such as Weapon.SlotNumber, Player.WeaponSlot, or MAPINFO's weaponslot command, so any actor or module using these more proper methods will be completely broken by setslot. This makes combining with other mods/addons essentially impossible.
Like I said, there's good reason setslot has been deprecated for
five and a half years.