Ahh, man, I'm just going to have to disagree with that one, I'm sorry to say. I loved Cata Heroics.
That said, I can understand why they'd be a bit much for some, even if I ended up even no-tanking or no-healing a few of them by the end, and commonly got through them even with DPS doing damage that'd have been slightly low even for a Normal mode run.
Granted, if they just hadn't allowed us to so overgear WotLK Heroics, I'd have been fine with them, too, even if the bulk of the difficulty back then was from people not knowing their rotations. The difference between their apparent difficulty on a fresh 80 and a year into WotLK were night and day, at least until the pre-ICC dungeon trio.
And Legion's Return to Karazhan was pretty brilliant, imo, when at-level. Mythic 0, especially.