He is building a long term legacy that will rival the greatest GMs imo. Sure, putting together the big 3 and winning a title could have been called luck to some extent, but you have to look at his other moves to see the brilliance. He has extremely quickly built an impressive set of assets to rebuild from the big 3 and unloaded them at just the right time. He got the most milage he could and still managed to get great value for them.
The real kicker though is when you look at his moves outside of our contending period. When he first took over and cleared out the junk that was left behind from the previous regime, he still managed to directly contribute to the end of the Lakers dynasty by facilitating the Sheed trade to the Pistons.
Now, while we are rebuilding again, he once again manages to end a dynasty and take down Riley by facilitating the move of Lebron to the Cavs. So even when he is in rebuild mode, Ainge manages to influence the potential outcome of the NBA finals and end dynasties, all at the same time as scoring points over the Lakers and Riley.
At fist I thought this may have been a coincidence, but it is now a regular pattern, and I am truly in awe. I can't wait to see what he does next.