A reason to kill mobs in dungeons
This would also make some classes more effective in dungeons.
They could do slayer and vanquisher modes and titles like they did in the first game. There would have to be a good incentive to continue doing it though. Once people get a dungeon cleared and have the title for it, they will go back to skipping like it is now.
Or they could just makes the mobs mostly unskipable (like fractals), I’m sure speed dungeon runners would love that.