Not to put everything at Jusuf's feet because I sort of assumed he was an afterthought in the trade with Denver in the first place and cautioned people at the time not to expect too much. But once he flashed a level of dominance that he did, it suddenly reset expectations and seemed to provide a path out of the spiral of mediocrity the team was locked in. Him regressing to the mean isn't the primary reason the team has backslid, but by being "just OK" they don't really have any shot at being something better than what they are presently -- it means that we're right back where we were last year before the Nurkic trade: A bloated payroll, a bunch of journeymen, and a couple of guards that are very good and pretty good offensively (Damian and CJ respectively) but are inadequate defensively as a pair to ever seriously form the bedrock of a championship team.
So no, I don't blame Nurkic for the team's overall performance; Turner, and Harkless have been much more disappointing (for instance), but his erratic and sloppy play have been a pretty reliable bellweather for the fortunes of the team.