The 1.12 Talent trees = higher dps/hps than what was required.
Multiple patches that also nerfed some raids: Patch 1.5
Molten Core: Lava eruptions (lava splash) only occur while Ragnaros is in combat, but occur less frequently, do less damage, and the damage they inflict is now resistible.
The difficulty for the current raids and many dungeons, its clearly not what it was supposed to be in phase 1