I don't know Monos, I don't know if he's "right" and/or has an axe to grind, so all the comments should be taken with a grain of salt.
No team is perfect but it's clear the Bills are a Top 3 team, and could have won the Super Bowl each of the past few years. That doesn't happen by accident, and while the Bills have come up short, it seems counter productive to just point out flaws in a team.
I'm not here to shill for Beane, but he has a great record.
He's built a outstanding offense, developed a HOF QB, has an outstanding OL, terrific RBs, some very good receivers and TEs.
On defense, Beane has brought in and drafted many very good players at Safety, LB, and CB. Two All-Pros and many pro-bowl caliber players. The downside is that the DL hasn't gelled. It happens, but it's not for lack of trying.
It's very difficult to be great at every position at the same time. Injuries, age, personalities, etc. all play a part. Eagles and Chiefs have their flaws as well, sometimes you can overcome, but there are too many variables to say that Bean and Company don't have what it takes to win a Super Bowl