I think the main issue keeping BLU out of roulettes and Duty Finder in general is that, since you have so much freedom with the spells you can assign yourself, you would end up getting BLUs with very few spells, or BLUs with spells that are not helpful or relevant to the task. I'm not sure what the best way to make it work and not be frustrating would be. But I definitely agree that it's a bummer to be locked to PF.