Your conclusions seem right. My old team went from B- to B (
http://whatifsports.com/hd/TeamProfile/Ratings.aspx?tid=13759), which I think is very generous. Meanwhile, my new team went from B- to C (albeit, on a 0-27 season) in the ACC. I don't remember seeing this kind of 2/3 letter drops before the change.
All in all, the new prestige system looks better than the old.