I don't think he's a quitter. He has a national championship ring - committed to the cats without even seeing the campus, IIRC - he just realized he was going to be limited at UK - and instead of accepting a role like Willis, he decided he'd be better off on a different kind of team.
Look, its not like we've suffered in recruiting filling his spot - IMO, he wasn't going to be a difference maker with a James Young or Devon Booker around
A lot has been made of Kyle's lack of defensive prowess. However Young or Booker weren't ever going to be on anyone's all-defensive team either. Maybe they could guard a fence post.