TP to Nick for the nice thread topic.
For perspective I've put those picks in context by listing the three guys taken after the one Ainge took. These are the best comps in terms of what other GMs valued in the same draft, at the same slot.
2010
Avery Bradley (James Anderson, Elliot Williams, Craig Brackins)
Luke Harangody (Pape Sy, Willie Warren, Jeremy Evans)
2011
JaJuan Johnson (Norris Cole, Cory Joseph, Jimmy Butler)
E'Twaun Moore (Chukwudiebere Maduabum, Targuy Ngombo, Ater Majok)
2012
Jared Sullinger (John Jenkins, Jared Cunningham, Tony Wroten)
Fab Melo (John Jenkins, Jared Cunningham, Tony Wroten)
Kris Joseph (Ognjen Kuzmic, Furkan Aldemir, Tornike Shengalia)
2013
Kelly Olynyk (Shabazz Muhammed, Giannis, Lucas Noguiera)
Colton Iverson (Arsalan Kazemi, Joffrey Lauvergne, Peyton Siva)
2014
Marcus Smart (Julius Randle, Nik Stauskas, Noah Vonleh)
James Young (Tyler Ennis, Gary Harris, Bruno Caboclo)
2015
Terry Rozier (Rashad Vaughn, Sam Dekker, Jerian Grant)
R J Hunter (Chris McCullough, Kevon Looney, Cedi Osman)
Jordan Mickey (Anthony Brown, Willy Hernanogomez, Rakeem Christmas)
Marcus Thornton (Norman Powell, Arturas Gudaitas, Dakari Johnson)
2016
Jaylen Brown (Dragan Bender, Kris Dunn, Buddy Hield)
Guerschon Yabusele (Wade Baldwin, Henry Ellenson, Malik Beasley)
Ante Zizic (Timothe Luwawu, Brice Johnson, Furkan Korkmaz)
Demetrius Jackson (AJ Hammons, Jake Layman, Paul Zipser)
I think the best apples-to-apples comparison is to ask how often Ainge ended up with the best player in the group ("Win"), how many times he ended up missing on someone "(Loss)", and how many times it was a tossup ("Draw").
I suspect that opinions will vary there based on everyone's perceptions and biases, so I won't show my own personal evaluation. But I can say that based on my personal evaluation Ainge has won these picks at about on average rate.
It is fair to say however that his two big losses (Butler and Giannis) are far more substantial than his clear wins (like Bradley).
On the flip side, I think that if you look at the best picks he's had (Brown and Smart), those are certainly not losses and could in fact end up being clear wins in both cases.