Ainge had a great career here. The turning point IMO, sadly, was the night Gordon Hayward broke his leg. I thought that team was built to compete with the Warriors, I really believe that.
Some of Ainge's best moves:
Ray Allen trade (hated it at the time)
KG trade (hated it at the time)
Kyrie trade (we can debate the long term impact, but it was a great trade at the time)
Create cap space to sign GH
Sign Horford
Trade down and draft Tatum plus get Kings pick
Trade Jeff Green that created the Memphis pick
Draft Terry Rozier
Draft Jaylen Brown
Draft Marcus Smart
Draft Pritchard
Trading for Isaiah Thomas
Brooklyn trade!!!
Biggest mistakes IMO:
Draft Yabu (in fairness, this draft from 16 on was very weak)
Draft James Young at 17 (some decent talent taken that year after that pick)
Trade rights to Desmond Bane (should have just kept Kanter)
Signing Kemba as FA (I supported this at the time, but it was too reactionary in retrospect, and costly)
Failing to trade Kyrie when it was clear (to us) that he wasn't coming back; trade deadline 2019 I suppose.
Failing to recognize until too late that Anthony Davis was not going to come to Boston (i.e., the moment he signed with Klutch!)
Failing to consolidate 2018/19 roster; too many mouths to feed.
I may have missed a few, but to me the plusses far outweigh the negatives. It was a great run by Danny. A lot of creativeness, and unafraid to take risks. Lady luck just wasn't on his side in the end (KG injury, Hayward injury).