During afflicted week when posts were made about it being poorly designed, the most counterpoint was that it was fine that certain classes couldn’t interact with it because the healer always could. The most salient post was probably from a person questioning what they were supposed to do when themselves and three friends consisted of a blood DK, rogue, hunter, and warlock and they PUG a healer. Yes in theory the healer could handle every afflicted, but in cases where the healer wasn’t the greatest or during pulls where they didn’t have a free global, there really wasn’t much else that group could do.
While most groups formed for the context of a key will happen upon a viable group comp that doesn’t leave it all to the healer, there are times when it can still wind up on their shoulders even without intentionally trolling with the group comp.