How do we even know it comes from Blashill? Seems like he runs the Dmen, but the system would come from Cooper.
Blashill took over the defensive side of the team and its been reported he took over structures and defensive game plans (moving to the zone defense from man). LaLonde focused on that when he was on the Lightning staff. Reportedly the system was changed based on the size of the roster which got smaller and maybe it's simply growing pains in adapting, but it didn't look like it improved tremendously during second half of the season or playoff stint except Vasilevskiy started returning to form. Blashill also didn't have the best track record in Detroit and defense was his focus as well both at NHL level and at Grand Rapids - what defenseman has Detroit really developed out of that system when he was running things? Why didn’t Detroit improve defensively year to year under him yet still remained closer to bottom of the league in team defense.
The whole team has struggled to adapt and maybe they'll have it down better starting next season. At least Vasilevskiy won't be dealing with his injury/back surgery and can help bail out the defensive lapses so it will mask it more (hopefully). I don’t know, but it doesn't inspire confidence, particularly with the "depth" we have due to cap crunch. And can definitely help explain Perbix's step backwards in his "sophomore" slump - maybe he gets more comfortable with the new system and takes steps forward, or maybe it was Perbix just hitting a wall regardless of system (and it's more he was playing above his expected level last year).
The poor defensive play of the team coincided with the changes although of course that has to do with roster makeup as well (and Vasilevskiy recovering).
But it wasn’t fun to watch, and Blashill was shown the door in Detroit for a reason (although being given plenty of time to fix things).