Yeah he was pretty overrated, but not anymore. He's lost his magic. Ainge, on the other hand, is still very overrated... at least for now. Everyone singing his praises right now, but soon, he'll do something irrefutably stupid, and there will be a thread titled "Is Danny Ainge Overrated?".
The fact is that all GMs are basically equally decent at their jobs. There are a couple notable exceptions, like Chris Wallace (sucks) and whoever is running the Lakers, I forget his name, (good), but otherwise its a level playing field. The rating of all GMs just depends on what they've done lately. Everyone loved Kevin Pritchard... but then it came to light that he was an arrogant tool. So now he's considered overrated. It's a boom-bust cycle. One day someone's overrated, the next underrated, and then a week later, they're overrated again.
For Dumars, the Iverson trade was "bust" in the cycle. If he ever trades for a legitimate center, that will be Dumars' "boom" and he'll be right back on top.