I think you underestimate the humans of azeroth too much. Some of the humans are actually pretty stronger, they do have titan heritage after all like for example Tarlo Mondan:
Tarlo Mondan had been at the Pandaren campaign from the first call for volunteers, and he’d been in plenty more battles before that. Orcs, moldering undead, twisted horn-heads that wore human skulls—he’d fought them all and lived.
He was for all account just a regular human. and not so regular humans can be pretty strong on their own: Kerri Hicks - Wowpedia - Your wiki guide to the World of Warcraft (fandom.com)
Also, Varian happened to be blessed by a Wild God. He could easily match most orcs strength for strength and did so against Garrosh.