More than few people said KC was criminally under-rated as a coach because he was not of the Pat Riley "Look at Me!" style of modern coaching. When cameras first came into huddles KC looked bad when his assistants were talking and he was quiet. Often we remember where we ended up, not how we go there. The phrase "Cancer on the team" was I believe originally coined to discuss Dennis Johnson before he came to Boston. McHale was the original "black hole" and Bird's trash talking confrontational ways were often out of control, as he admits now when discussing his fight with Dr. J. When the 84 aqnd 86 Celtics won there was a legitimate GOAT conversation going on about Bird, and the "Slow White Guy" dominates Black Super-athletes narrative did not leave much air in the room for an understated selfless black coach.
Red also had no problem inserting himself in the public eye, and when VHS coaching videos were hitting the market for the first time Red had himself, not KC on the court with Celts.
Russell says KC was a big believer that his job was mostly done before the game, and despite his pedigree as part of the greatest dynasty ever, saw letting Bird put his stamp on the team as the way to win. I think the line was "KC wants rings, not credit." He was not one to insert himself at the front of things. He is also given top marks by more than a few people for helping black Celtic players deal with the best two players being white guys, and how fairly or otherwise the Celtics were seen as white America's team.
Thinking of the Patriots, today imagine how badly people outside of Boston wanted the Celtics to lose. When Cousy left it was assumed, and hoped for, the end of the run. But they were if anything they were more dominant. So perhaps KC was over rated as a player because of that. But it is also possible that the people that were around then, that gave him a big part of the credit for how the Celtics fast break ran, how their defence sparked the offence appreciated something about KC the player we will never understand.