Yep, the Bills were certainly fortunate to land Allen.
In reality, doesn't it seem that there's usually 6 or 7 standout QBs in the NFL? It's kind of cyclical. The Packers had Favre & Rodgers back-to-back, highly unusual (and "only won" two SBs with them).
Of course the flip side there's teams that haven't had QBs for a very long time. Erase Mahomes from KC for example, their last long-term good QB was Len Dawson.