I tend to side with the knee-jerkers on these types of posts. Is it holding Ainge to a very high standard? Probably, but I can't remember a title team besides the Heat that didn't knock at least one late pick out of the park.
The Spurs title teams post Robinson were fueled by absolute steals in Parker and Ginobili. The Warriors got a star in Draymond Green in the 2nd round. The Celtics obviously got two huge parts of their title squad in Perkins and Rondo, and only got Garnett because we had Jefferson. Unless you are lucky/crappy enough to build your team primarily with multiple early lottery superstars/picks (Cleveland, Oklahoma City), finding steals in the draft is really important.
Fortunately or not, free agency and tanking don't look like possible options for us right now. That leaves trades and making the most out of late picks. Thankfully trader Danny is still winning practically all his deals. He hasn't gotten a hidden gem in the draft since Rondo though.
Yes, he's drafted some nice role players and that's fine and dandy, but these guys aren't going to be the centerpiece to any deal for a star and after four years the decision whether to keep them comes up. Once they get deals that are closer to fair market value they cease to be bargains and might as well be free agents we picked up.
In conclusion I think it's fair to say Ainge hasn't drafted poorly but also hasn't been amazing the past 8 years or so. It would have been nice if in that time we had gotten a huge steal like say a Giannis or a Butler or a DeAndre Jordan (all players taken within 5 picks of a pick we had). Is that too much to ask? Maybe, but just one steal like that can mean all the difference.