I haven't downed this fight on HM in fact I have only attempted it once, but it seems that this fight on HM is still not a dps race. The berserk timer is still 10 minutes. On normal mode we usually finish this fight with about 4 minutes left on the berserk timer. The hardest part about this fight isn't the healing - hell if it weren't for frost tombs in phase 2 (or 3 for those who count the air phase as an actual phase) this could be 1 healed on normal.
The major issue I have seen with this fight on HM is the fact that some people just don't grasp the concept of "You are damaging the raid with unchained - GTFO". Unchained when it goes off (backlash) with 8 stacks, hits everyone in a 20 yard radius for ~10k - that shit hurts a bit, whether you have a resto druid or not. If you have AVRE, you know how big that 20 yard circle is, if you don't I suggest you get the mod specifically so you can see how big this circle is. Another issue I have seen (and it is very apparent in the logs posted in this thread), that people don't understand the concept that frost tombs are not survivable unless you are a tank. They hit me for 200k in tree form. There is no "oops, I forgot to move - heal plz". Simple concepts are what kill people on this fight, not bad healers. If your healers need to all be pulling 5k HPS, that means you need to look at why the raid is taking 15k damage per second.
As far as hero goes? Phase 3 = win for hero. Sure you have more dps on the boss during phase 1, and have less air phases, but phase 3 with hero means those frost tombs will be taken down faster, not to mention shortening the phase due to more dps. Healing in this phase is very stressful, and the longer you are in this phase, the more taxed your healers are going to be.