They've been terrible at the draft, regardless of draft pundits grades. They've been terrible in handing out large contracts to some players (Dareus, Glenn, Clay) which leads to not keeping solid players that wouldn't brank the bank (Hogan, Gillislee), and letting high round picks move on after their rookie contracts (Woods, Gilmore). They then draft players to fit a particular scheme and then abandon that scheme (Ragland). They empahsized the WR position throughout Whaley's tenure without anything to show for it on this year's roster. They did a terrible job of building franchise anchors for the team through the draft from 2013-2016 - Manual, Woods, Alonzo, Watkins, Kuoandijo, Darby, Ragland are all gone - only Preston Brown, John Miller, and Shaq Lawson to show for on the current roster as potential starters and I don't think anyone is thinking Pro Bowl calibre player for any of them.
I thought Doug Whaley was good at acquiring players through FA and trade, but was absolutely horrendous at the draft. The team was left with bloated contracts and a dearth of young talent. You could see this year coming sometime, Beane and McDermott just accelerated the inevitable by trading away the best of the young talent that was about to get expensive for draft capital. It remains to be seen whether that was wise, but I'm very skeptical. There are plenty of ways to suck at personnel decisions - so taking a different direction doesn't mean the destination will change. I think the Darby trade really wasn't wise considering he was cheap this year, and they could have extended him after a sophomore slump at a discount. If they are really interested in getting this team in the right direction, they should be more focused on cleaning out the bad contracts and keeping the young talent.
I think that you are right about coaching to some extent as well. The Bills have had some of the worst player development in the league for many, many years. You know this is the case when guys are showing a ton of promise in their rookie seasons and then not improving. This has something to do with the constant turnover as well, but of all of the coaches they've had over the years, Roman/Lynn and Schwartz were the only ones that seemed to get more out of guys as they became more familiar with their schemes. I think the Offense is going to regress significantly this year, because Dennison is not an adaptive OC (i.e., he runs his offense regardless of whether the roster is full of square pegs for the round holes). WIthout an adaptive OC (e.g., Lynn, Roman, Gase, Shannihan) - Tyrod is likely going to struggle doing things that don't fit his skill set as much as the Offense he ran the past two years. I hope that I'm wrong, but that's the way I see it playing out.
The Bills have had a pretty good offenses the past two years, and pretty bad defenses. Before that they had a pretty good defenses for two years, and pretty bad offenses. Are we ready to do another switcheroo - I think that is going to be the case this year - Pretty good D, pretty bad O.