It took five months between release of Molten Core and world first Ragnaros kill. Five months! Mythic Jaina took less than a week. If you count Heroic as the release, Jaina was still only a couple weeks.
More debuffs will help a lot. Knowing the fights will help. The availability of tier 0.5 will help with MC. But classic raiding difficulty will still be at least as hard as mythic is now.