I see locked loadouts as a way to increase difficulty on endgame activities. If once you enter an activity you had to stick with your load out until the end of the activity it would definitely make me and my team think about which roles we'll need to play. Do we all want to run sniper rifles? Should some of us run launchers for crowd control? Maybe a few of should run shotguns? What primary is best? What element should my energy weapon be? What kind of enemies will we be facing and how do we counter them? Newly introduced elements don't have to solve issues, they can also be used to increase difficulty.