I think when looking at how much better the teams in the afc got, you have to look at the whole offseason.
this is a quick, vague overview:
Pats*
biggest needs: pass rush, pass rush, pass rush. also saftey, linebacker, and oline with light retiring.
Key additions: Brandon lloyd, Gonzalez, hightower, chandler jones.
key losses: light, anderson, carter (?)
Bills:
biggest needs going into the offseason: pass rush pass rush pass rush, LT, depth, CB, WR.
Key additions: Gilmore, Mario, anderson, glenn
Key losses: Bell
when you look at the offseason as a whiole, all afc east teams needed pass rush, and bad. it is obvious the bills pass rush improved way more than the others. Jones might turn out to be a good player for the pats*, but they also lost a 10 sack player from last year (to us) as well.
I think looking at the whole offeason, the bills improved more than their rivals. Sure, it might not be enough improvment to make us the best, and it has to be proven on the field. But I say if we had a top ten QB (Brees, Eli, Rivers) we would be division favorites. We can still win and do well with fitz, but if we did have a top ten QB, it would be hard not to have super bowl expectation for this team, imo.