It’s a game of builds and you restrict players to certain builds and mods by forcing costs on replacing and swapping mods each time. When you get RNG gift you the right exotic armour, the right roll you have to pay to swap out mods. Some game modes require higher super use. Make mods interchangeable so you can pick which one you use. Some game modes you get one super per set so makes more sense to run grenade or class. Once it’s added you should just be able to swap out mods. Or remove them without any cost.