I think there's a difference between viewing the trade as yielding little in return, and viewing Ainge as having screwed up.
It's been said over and over, but the market for Rondo was just not there, for all kinds of reasons. So, we didn't get a whole lot back. But I don't think that's Ainge's fault. Nor can he really be criticized for waiting too long. Once Rondo tore his ACL the outcome was largely out of Ainge's control...as low as Rondo's value was two days ago, it was probably even lower last year, and Ainge benefited by waiting to see whether "peak Rondo" would return.
We may all have been spoiled a little bit by the KG/Pierce/Doc trades, which in retrospect seem like big winners. But there aren't a lot of crazy GMs out there these days, particularly running contenders (which were target teams for Rondo).
I'll reserve judgment on Ainge's performance this year until we see what happens with Green, Bass, Wright and the other players he is probably trying to move as we speak. Green in particular is intriguing as there are fewer good SFs than good PGs right now, and there are several contenders looking for help on the wings.