That wouldn't fix it, it would make the dungeons even more of a faceroll than than it is. Most of the "Easy" dungeons can even be done with only 3 players, though take significantly longer. Even under some circumstances you can finish a dungeon with just one caster who has a healing magic and one tank. These are really fringe scenarios.
Like the correct fix for this is to queue for the roulette dungeon with any available job the player has, instead of players having to select Tank, Healer or DPS beforehand and then have to sit in the queue for 20 minutes when another job may have an instant-in. To give you an idea, nobody actually queues for roulette unless they are doing the daily reward, and could quite honestly play them with whatever they have at the appropriate gear ilevel. When people "need" a specific dungeon, they queue for that dungeon with the specific job they need.