It's a combo deal, in my opinion. That's one part of it, but they also severely botched the offseason work. Miller/Pettersson have coexisted without public incident for extended periods previously, largely when the team was winning. The blue line's complete inability to transition/move the puck is hampering everything offensively, and is probably extremely frustrating for the forwards. Fingers are being pointed etc.
I somewhat wish management would just come out and say, "Hey it's on us, we obviously didn't bring in enough defensive depth, specifically puck movers. It's impacting the forwards and our ability to generate offense, but we still believe in the forward group and we're going to fix the blue line to get back to our winning ways." Instead they leaned into this Miller/Pettersson thing and throwing mud at the forward group, and it's created this massive issue, plus Pejorative Slured their bargaining position if they were to choose to move anyone.