I think that's as intended; in normal mode you don't have to worry about enrage, while in HM you have a 5 or 6 minute enrage while having to deal with the increased complexity of the computer system and each of the three "jets", as we call them, do different things. If they upped the HP from in HM from what it was in normal, they would have to increase the enrage timer or change some of the mechanics of the fight to make it easier.