Yadda yadda.
I've talked about Ash's faults in this before, but his mistakes were largely in hiring. Mehringer turned out to be a bad choice in retrospect (head-scratching hire turned into headache). This was compounded, though, by not hiring an experienced offensive coaching hand to be a mentor/backup to the supposed wunderkind... so there was no one one to turn to when the offense started going south, and Ash didn't have experience on that side of the ball to right that ship.
Given Ash's lack of experience on that side of the ball, one would have hoped he'd have hired a strong OC with a proven track record that he could trust to own things as he acclimated to the HC role. Obviously, he went a different direction, and that decision had him stumble out of the gate.... no telling yet if he'll be able to catch up to the pace of the race.
Ash wasn't going to be able to step in and start calling offensive plays, though, as that's not his skill set... and if Mehringer was sidelined, there was really no one else on the offensive side of the ball who could, either. So, 100% agree that the root cause of the problem lies with Ash (hiring)... but once that mistake was baked in, there wasn't much he could do to fix it once the season started.