I largely agree with CoachBo above. The first problem in the OP's argument is that the 2007 players we traded away never amounted to anything. Even Jefferson has proven he can't be a core building block of a championship team--and he was far and away the best of the lot.
On top of that, while KG and Ray were not homegrown, they were everything that Celtics were supposed to be and it transformed the team into something reminiscent of Russell's dynasty in the '60s where defense and team came first every night. While I'm still bummed about KG going down in '09, Perk in '10, and Shaq in '11, I constantly reminded myself during the entire time that this is exactly how basketball should be played and it was a thing of beauty.
But my biggest problem with the OP's post is that there is somehow a right or wrong way to build a team. The only "right" way to build a team is to gather as many assets as you possibly can and make the best use of them depending on the hand you're dealt. Sure, in theory, homegrown sounds nice. We can all watch the youngsters grow up and develop and eventually be a dynasty. It sounds great on paper. But what happens, if say, you end up getting the #5 pick in the draft instead of getting the #1 or #2?
I'm sure Danny would have been happy to build around youngsters if he landed Durant, but that's not the hand he was dealt, so he made the best of the one he was. And that's a sign of a good GM.
Personally, I don't care how he does it again. Build up the youngsters, repeat the KG/Ray formula, or do something in between. But no matter how he does it, I hope it happens sooner than later, because watching these games isn't fun.