To be Honest i found the BC Heros a lot Harder, at least some of them. Shattered Halls used to be Really fuck you up with that 7+ Mobs at Once Trash Groups and so on.
I also Remember back then mob groups draining me oom because i had to Shift out Of Tree Form to get rid of Poison everytime because you couldn't cure poison in Tree Form. Shadow Labyritnh was also really Tough at the Beginning. Not to forget the "one hit" Meteor Trash in Arcatraz
So i realy like the Difficulty of Cataclysm Heroics.