IIRC, very few thought the 2008 Cs could get things together quickly and gel enough to win a title. Doc got them to do it. Yes, KG was important, and yes, Thibs was a great defensive coach, but when you win,especially with a team of almost all newcomers, the HC gets a lot of the credit.
I've been following the NBA for almost 40 years. Doc did a tremendous job in 2008, and badly out-coached Phil Jackson in the Finals. i would have liked another title or two, but i don't blame Doc to KG or Perk's knee injury or for breaking up the "starting lineup that had never been defeated in a playoff series."
He didn't want to coach a rebuild, and I don't think ownership wanted to pay him to coach a rebuild. Time to move on. he's going to talk up his new team, as he should. I'm not going to diminish his contribution to the last half-decade of Celtics basketball. Every game, my team could get a win, and that's a great thing for a fan. I hope that happens again real soon.