That is exactly what was happening IMO. Maybe through their own ignorance or just not understanding that a players development is not on a constant liner path upwards. Humans can take 3 steps forward, 4 back, 2 forward, 1 back, 6 forward, 2 back.... that is life. No difference for Marner, he is going to have gains and set backs.
I do think that omissions of effort are legit areas you can criticize him for, early in this season. There were times when he really lally gagged his way on the back check, that is not a skill thing that is a will thing. In a competition sport lacking the will to compete is inexcusable, for anyone, no matter what age you are.
Onward and upward, he seems to have found line mates he clicks with , that compliment his skills and his warts, if this is how good he is at 19, how good will he be at 23? 27?