The impact coaching has on a team is subtle and intangible with the overt and tangible being a, relatively, miniscule part. The players have a substantial impact on the success of a team, so it is difficult to distinguish where the line is drawn.
Doc’s teams have underperformed on too many occasions to continue to excuse him by blaming the players. Too often during Doc’s tenure as HC of the Celtics, inferior teams would make games and series more difficult, regular and post season.
Also, for a “player’s coach”, chemistry issues have been a question on several of his teams (Rondo vs. vets, Bradley vs. Ray, Paul vs. Blake and DJ, 2020 Clippers).