It's both, but Wilks will end up being the scape goat for all of this among the fans. I still maintain that this roster wasn't going to the playoffs no matter who the Cardinals brought in to coach it. This team was doomed from the beginning.
In 2017 the Cardinals had the oldest roster in football as the Cardinals made one last push to win a SB before the window closed on that roster. That last push delayed the inevitable rebuild that the Cardinals had been ignoring for years.
Many fans claim that this is the same group of players that Betcher had as a top 10 defense last year. However that is far from the truth. Gone are several key Veteran Leaders and starters (Dansby, Rucker, Mathieu, Branch, T. Williams) which forced Wilks to rely on young unproven players who the previous regime drafted in 2016 and 2017. Aside from Budda Baker those young defensive players had looked like busts and to this day still are major question marks (Nkemdiche, Reddick, B. Williams).
Then you move to the offensive side of the ball which is worse than the defensive. This team started the season WITHOUT a single QB on the roster! That is insane! The Cards tried and failed to land any of the top FA QBs that were available and settled on the trash that was left.
The Cardinals were able to move up and select their QBOTF which was a great move. However in doing so the Cardinals were looking towards the future and ignoring the present. They used their first 4 draft picks on offensive players and completely ignored the defensive side of the ball that also had major holes to address. It was a calculated decision to surround Rosen with some young talent so they could develop together. I think it was the right choice but again it ignored the defensive side of the ball.
The offense also was built around an OL that had 4 starters coming off of major injuries and all of whom also had a history of injuries. So is it shouldn't come as a surprise that injuries have taken a toll on this OL.
IMO the biggest mistake of the offseason was the signing of Mike McCoy. This set the offense back an entire year and didn't help develop our QBOTF any.
Yes the Wilks and his staff hasn't elevated this team with coaching, but I think they were behind the 8 ball from the start.