I think the issue lies elswhere: People treat roulettes as "random dungeon wheel" that they do purely for fun. When it is clearly game's way to fill up queues for people who queue for particular duties, thats why you get rewards for the roulettes.
Thats why i think the solution is to rename current routlettes into for example "leveling daily duty" and have in the description the purpose of the duty. Up to consideration if full premade would be blocked. Of course such duty would put massive priority on people queueing for regular duties.
On top of that i think introducing a proper "dungeon/raid roulette" that would just be the for fun would be cool (im not implying regular roulettes cant be fun, but its about the main purpose)