Here are the key transactions that have led to titles in every season since the last time the Celts were plausibly in contention:
2013 - Heat draft Wade in 03, sign LeBron and Bosh in 10.
2014 - Spurs draft Duncan in 97, draft Manu in 99, draft Parker in 01, draft Kawhi in 11
2015 - Warriors draft Curry in 09, draft Klay in 11, draft Draymond in 12, signed Iguodala in 2013
2016 - Cavs drafted LeBron in 03, drafted Kyrie in 11, traded for Love in 14, re-signed LeBron in 14.
2017, 2018 - Warriors signed KD in 16
2019 - Raptors traded for Kawhi in 18
Which of the above should Ainge have been in on?
Is it Ainge's fault for not signing KD in 2016? Or does Ainge deserve credit that the team even had a shot at signing KD just three years after blowing up the Big 3?
I think the only one that you can really fault Ainge for is not trading for Kawhi. Hindsight is 20/20 on that. A lot of GMs didn't want to take that risk. The Raptors had very little to lose. Kawhi ended up leaving them after one year just like many people expected / feared. If not for a few lucky bounces against Philly that trade might look like a really bad gamble right now.
The above is simply meant to underscore how silly it is to penalize a GM for not winning a title. Lots of things Ainge has done well and poorly. A lot of smart moves that did and did not pay off. A lot of misses that could have made a difference if Ainge had chosen differently.
But title / no title is a really dumb metric.