I believe it's Joshua.... The chemistry he has with Garland is pretty big and when you have the 3rd line running like that.... the others will do their job.... but the 3rd line being officially out of service.... not the same....
they've also had this coming for a while... half their team has shooting percentages that weren't sustainable, their first half schedule was way easier than the second half, and they've had precious little in terms of injuries until now...
there's also the matter of Petey being unsigned, and now being forced into mid-season negotiations under the blackmail of potentially being shipped out to Carolina (or somewhere else)... I get why they want certainty on this, but forcing him to engage mid-season can't be good for his game... if the public is hearing about this now, it's probably been going on for at least a couple of weeks, which tracks to when his play started to fall off...
they'll get through it, but there's also a reason almost every Stanley Cup champion has had to fail once or thrice before eventually winning... this is a roster that is woefully short on meaningful playoff experience...