OK I see what you're saying in that they are built similarly but the comparisons end there when it comes to skill
Cornerbacks:
The Bears' top 4 cornerbacks are superior to the Bills' unit BY FAR. Clements and McGee can stack up to their top 2 but as a whole, their secondary is a better, deeper unit.
Tillman, Vasher, Hester and Ricky Manning Jr
-vs-
Clements, McGee, Thomas and Greer
Add to it Mike Brown, who is a Pro Bowl safety, I think their secondary is frightening.
The D-Line, position by position, is far better and deeper as well.