I'm not going to get the pitchforks out until I see if things start getting back on track once at least one of these core offense guys comes back. Looking at the SportTrac injuy trackers for last year, there's a couple of interesting points:
http://www.spotrac.com/mlb/disabled-list/2017/washington-nationals/ <-- that's all the DL stints. At this point in 2017, Eaton hadn't been injured yet, Trea had a hammy issue and did a short stint and came back, and Stephen Drew was starting a long DL stint. Losing 10-15 days of Trea and 6 weeks of Stephen Drew isn't anything compared to losing basically half your offense for a couple of weeks and counting.
http://www.spotrac.com/mlb/disabled-list/2017/cumulative-position/washington-nationals/ <-- sorted by position, while there are definitely some big blows, a lot of the injuries were to the replacements for the already-injured players. Last year it seemed like left field was a weird ancient Indian burial ground whose protective spirit had been awakened and was now hungry for blood. So, yes, a lot of guys went on the DL, but when some of them are Ryan Raburn, Chris Heisey and Stephen Drew, the impact is not as extreme.
And while Dusty did a great job of steering guys around the revolving left field door last year, that's not any real guarantee that he'd be doing any better right now with the current injuries. The closest 2017 got to the current level of injury to key offensive players was the last half of August into September, when Bryce, Trea and Jayson were all on the DL. The Bryce-Trea-Jayson collective is not the same offensive powerhouse that Eaton-Murphy-Rendon are, plus this coincided with Difo's super hot streak, so we were still getting .313BA out of the shortstop position and we were able to go something like 12-8 during that stretch (although 6 or so of those games were against the 2017 LOLMets and the Almost LOLMarlins).
Time will tell how much of the current nosedive is on Davey and how much is on the half-AAA lineup we're trotting out there.
All that said... I think Davey is still learning the subtle art of bullpen management and we should know in the next couple of weeks if he's learning from his mistakes or not. I do think he's made some bad decisions that have cost a few games, but if he learns from them and does better going forward, time will tell.