It's more a content design flaw than it is a raw role balancing issue IMHO.

My old Resto/Elem hybrid Vanilla WoW Shaman was hilariously overpowered at some stages of the game (And I'm sure there are ex rogues etc here who can attest to the misery that was trying to kill a Shaman wearing Invuln. Mail/Green Whelp and loaded up with NDBs and Tubers, you simply weren't going to win, ever). Yet if you took 3 groups of 'me' and put them in Arathi Basin, we wouldn't be able to win because we'd never manage to actually take anything beyond the first objective.

1 healer vs 1 dps should be a stalemate, that's a fair balance. But the content should most certainly not 'reward' a group stacking healers above all else, that's just poor design.