They should have traded some of those "low spades" for a superstar in the off-season, while they had the chance. While their values were at an all-time high. But they got tricked by that run to the ECF, and convinced themselves that they were good enough.
Ainge made a lot of good moves, but he started feeling himself a little too much, and whiffed on the opportunity to turn some combination of Tatum, Rozier, Brown and/or Hayward + the Kings' pick into a game-changer.