I never did climb Mount Hyjal back when it was still inaccessible content. By the time Cataclysm rolled around, it was accessible by flying, so now my perceptions are skewed. This Mount Cortis feels taller than anything I've climbed, but there might be taller mountains in Pandaria or old world.
Thinking about it, I should take Edresi to Zandalar as well. I've seen some mighty fine mountains there.