If you look at the all the current NBA coaches, and sort by their playoff record - he ranks out 18 of 24 (or bottom 25%). When you take out all the coaches that have less than 6 years coaching experience, he's #16 out of 19 coaches (or bottom 15%). He's right on par with Nate McMillan...
You could MAYBE argue that he's an average NBA coach, but there is no way in hell that he's a top tier coach.
Kerr, Bud, Nurse, Spoelstra, Pop, Bud, Gentry, Brown, Vogel, Rivers, Carlisle, Casey, & Brooks are all clearly better.