As of right now, the Bills have beaten teams with a combined record of 1-5. And the one win came against a team that is 0-3.
I may be wrong about the defense, but you are talking about the Chiefs' offense and the Browns' offense. In three games, Cassel has been sacked 11 times and Weeden 8 times. Yes, the Bills got more than other competitors, but they are both highly sacked QBs. Cassel has 3 TDs (two came vs. the Bills) and 4 INTs for the season. Brandon Weeden has 3 TDs (one came vs. the Bills) and 6 INTs for the season. These are arguably two of the worst QBs in the league right now.
In terms of QB ratings, the Bills have faced the 24th (Sanchez and he had a great game vs. the Bills), 27th (Cassel), and 30th (Weeden) ranked QBs in the league. The QB competition that the Bills have faced is rather mediocre to say the least.
I don't think the Bills are the superior team at all. They may be better in certain areas (much better in some cases), but overall the Pats are the better team.
Also, in terms of defense, the Pats are the 14th ranked defense and the Bills are 17th. The Pats are 10th in points allowed while the Bills are 23rd. The Pats are 12th in third down percentage given up while the Bills are 25th. The Pats are first in the AFC in turnover differential (+4) while the Bills are 4th (+1). And the Pats faced better QBs at least in terms of QB rating (Kolb is 3rd, Flacco is 9th, and Locker is 13th).
With Spiller out and Jackson far less than 100%, I still think the Pats win this one big. If I am wrong, I will admit it. But I think Bills fans are overrating their team.