Where human is at it's strongest is a mounted build that runs 2 forms of mounted damage. For instance a mounted hybrid with both mounted melee and mounted magery or a MA/MC combo.
Roughrider gives 15 discount on ALL riding subskills. So in both those instances it saves you a total of 45 points. And activated abilities don't work from horse. This makes humans pretty strong in that context.
That being said, I do thing even so roughrider should get toned up a bit. A 45 point discount for a build ideally suited for it, and 30 points for the average build is alright but it's not a "YOU NEED TO PLAY HUMAN" sort of deal. I can make similar builds on other clades and they work fine.