Idk, I've never had any trouble playing against a disco priest in the arenas, when I was healing. I generally considered it a free win.
You just have to know when there's a good purge opportunity, and you'll wear the disco priest down in no time. Slowly but steadily you'll see the enemy DPS drop in hp first to 80%, then to 50%, then 30%, and executed, because the disco priest will have a hard time topping him up.
Eventually the priest will change his and his DPS partner's hp percentages, and that point, the disco priest will 9 times out of 10 get one shot if your DPS knows the basics ot changing targets ^_^
Idk, I really feel like priests are super weak in this patch :p
But go ahead and make one, just dont say I didnt warn you!
Regards,
Bear