I'm not quite as optimistic as you.
The offense needs at a minimum a QB, a deep threat WR, and a competent catching and blocking TE.
As far the the defense goes, with few exceptions every area except the line is suspect at least.
The Bills have done little during free agency, either by design or just not being able to get anyone signed. And they have 6 draft choices.
I'm inclined to call this another rebuild year and not expect much while Marrone and company get their feet under them and try and fill some of the holes much more than I would say the Bills are just a QB away from being competitive.