That depends on how they're killing normal Primordius. If they're zerging him and ignoring the blobs - yeah, that won't work with 75% damage reduction in heroic. Not that it's a huge change in strategy, but I can imagine it being harder than it would be otherwise.
we kill primoridius by killing the blobs that spawn. We killed it that way our first kill and then tried doing it the zerg way for a couple weeks but it was really boring so we went back to kill the blobs to get our buffs.
Primordius is very easy - it's really just tank awareness and the HPS/DPS check now are very easy. Megaera is very dependent on raid positioning as well as healing. If your ranged can't properly handle stacking ice beams on top of each other, the encounter gets very hectic.
Durumu is easier healing wise but requires the most coordination/raid awareness of the three.