Huh? You could do the boss before MoP, even before the prepatch for MoP... You could do LK probably naked right now at level 90, unless it's heroic mode you're talking about. A reason why you hit the enrage was probably because you used HotR for single-target or didn't purposely take more damage from stuff to get more vengeance (apart from the AoE phase).
It's great and all that you could kill LK, but that, Kel'thuzad and all the other extremely easy bosses have been done aaaaaaages ago. Once my guild is done with progress I'll probably get back to soloing a bit, going to try some challenges again (T11, T12).