He probably ended up only "higher side of average" but because of neglect in practicing his skills in the years since Hogwarts, only really using the Memory Charm. As for Wandless Magic, he'd have ot be on the low end of the spectrum to be completely incapable, as before mentioned there's entire societies of wizards who don't use wands. I'd compare Wandless Magic to learning to walk in a society where everyone has hover chairs from the moment they would otherwise begin to learn to walk. (Almost) Everyone CAN do it, but why bother when a hover chair is so much better?Huh, I had been under the impression that he was on the higher side of average, and so Wandless was simply something beyond him...
Well, since Pixie is going to have access to my Laptop after I go to work in about an hour and a quarter-ish that might very well get fixed.