As a tank, you only have so many cooldowns. I personally think you shouldn't have to spend both your 30% and your rampart on one large pack.

Now, who's to blame? The DPS, of course, but they're so brain dead most of the time there's not much you can do about them. Healers, I'd actually place more blame on them if they're not AoEing, and that's an enormous source of DPS. However, you should also look at yourself first and foremost. Are you DPSing like a champ or a chump? Depending on your answer, you may need to read up on how to fix that!