Throughout Mists of Pandaria we've been doing nothing but powering him up by giving him different things. Manifestations of Wisdom and Power, knowledge about the Mogu, knowledge about the Titans, the heart of the Thunder King, a spear empowered by a Lightning Serpent, stones filled with time magic.
And then there's the 5.3 quest where he needs to be physically disadvantaged or he'd easily kill us.
Wrathion is not a normal whelp. That is kind of the point of him.