You can go on WoWhead, or even open up the Dungeon Journal and compare the difficulty outputs to one another.
Normal → Heroic is a bigger jump than Heroic → Mythic.
Take AA for example: Overgrown Ancient
Normal
Health: 2.48 million
Tankbuster: 85k damage
Heroic
Health: 4.63 million
Tankbuster: 311k damage
Health increase: 86%
Damage increase: 265%
Mythic
Health: 7.08 million
Tankbuster: 938k damage
Health increase: 53% increase
Damage increase: 201%
Jump from Heroic to Mythic is less than the jump from Normal to Heroic.
Apparently I am? Who knew
many people reinforce what I say. Are they all my alts too??