You do get a small achievement for completing all the leves for each class. Doesn't reward you anything, but there are actually achievements. =p
(when I went to look up all the battle leves, I found some people listing a few that literally never show up. Not sure if it was a 1.0 thing or what, but for a while I was a little disappointed that I wouldn't be able to do all of them if some were bugged and never rotated in)