I would rarely use diversion except against spikers (not on monks) but blackout is a must against boon prots, who's spells are so difficult to interrupt (doesn't stop me though)
. Imo blackout just has more applications of useage than diversion, although diversion is good, its just not as good as blackout for some particular scenarios (e.g. against monks). Langour, sure they made it better, but I just don't think its worth the elite slot. So what, lessen a monks energy by 10. They'll probably never be near full energy anyway, always around the 20-30 mark as they spam skills and use energy management. Imo langour is just out shadowed by soo many better elites (renewal ftw !!!).
I think the blackout vs diversion arguement could go on for a long time with everyone adding their part, although after awhile patterns of similar builds using each skill in similar scenarios will appear. Fine if you've got a build where diversion works better than blackout, thats great and vice versa. In Gvg teams that use 1 mesmer, you often seen a diversion mesmer and he works very well but only really for support against non monks e.g people who are less likely to be expecting diversion e.g. warriors. For straight up shutdown, blackout is by far more effective.
Langour will stay unlocked for me till Jupiter has a McDonald's on it


So players don't bother asking for removal, they choose the simple (and best imo) solution : pick a spell and cast through.