The inability to grasp the proper use of the replay challenge system, like the well-demonstrated inability to manage the game clock, speaks volumes about the general inadequacy of Rex and his staff. In a league which is designed, through the salary cap and the draft, to tend toward personnel parity, it's essential to maximize non-personnel-related opportunities. Those are the margins on which most games are won and lost.
By and large, Rex and his staff have failed in this regard. While initial game plans on offense and defense have generally seemed sound, any advantages that the Bills have won through early game tactics have dissipated later on; there's no arguing that they routinely find themselves outmanoeuvred by opposing coaches' in-game's adjustments. And the below-average performance in clock management and taking advantage of replay further compounds the problem.
In short, we're usually outcoached in most aspects of gameday management. And while I think that the player personnel is pretty good - probably above-average - it's not so superlative as to overcome Rex's staff's inability to win along the margins.
The worst part is that Rex has been doing this long enough that there's no reason to believe that he's going to learn and evolve. He is what he is. And I sincerely doubt that what he is can lead a team to a Super Bowl in today's game, or even to sustained winning seasons.
The REAL worst part is there's no way the Pegulas move on from him until the end of next season, at the earliest.