Quin was part of the team and shares in the blame/problem but I wouldn't place as much blame as you are. Coaches have different strengths and weaknesses and crazy part is Quin has multiple degrees at Duke, double major in
philosophy and
political science, and, later received a
J.D. degree from
Duke Law School in 1995 and an
M.B.A. degree.
https://en.wikipedia.org/wiki/Quin_Snyder
So maybe his style no longer fit or meshed with what the team had grown into and he even eluded to a big in his exit press conference that he felt the team had the talent but needed a different voice.
To me it was no one thing but a collection of different things that just all added up.