Currently, we can only alternate between 4, why not more?
I don't see a problem with extra weapon slots, as the weapons still take up inventory space so why not have the extra functionality of more weapon sets, for pvp it would be great, and pve, not as necessary but handy
you can just double-click the item you want to use in your inventory and equip it mid-game. Sure a weapon set would be faster but it doesn't matter. You can still do it and it takes like half a second longer.