I think there is a lot of blame to go around. The reason his system worked is we outscored all of our problems. We had a an excellent top 9 and Burns and later Karlsson benefited from taking shots from the point and having Pavs being so good at tipping it in.
However, last offseason we lost Pavs, Donskoi, Nyquist, and even Braun. I think we can all admit that the system gave up tons of high danger chances and our goaltending was not up to bailing us out. That was fine, when we were scoring a ton of goals but after losing those 3 forwards and having Sorenson regress, Thornton age 1 more year that we no longer had the horses to successfully implement PDBs system. PDB never really adjusted to our personnel having less firepower. Added to the teams horrible chemistry problems out the gate and starting players who clearly weren't ready to play we were in a lot of trouble.
Once the injuries hit at the end of the year we were done no matter what system we used. But we were in trouble long before that.