I read somewhere that DA's biggest draft regret isn't GA. (It was Butler.) He said that they had seen GA plenty and they considered him but thy never saw him as an all-NBA candidate. KO was a good solid line drive to CF. GA turned out to be a Grand Slam but he also could have been Bruno Caboclo.I think we are talking past each other a bit. I evaluate this as two distinct issues. First, did the player you drafted end up being a good value for their draft slot? Olynyk easily did. Second, are there other guys that you should have drafted instead? Obviously, yes.
As examples from the same class, Bennett was a terrible pick. Oladipo was a very good pick. It doesn't matter that even with his breakout he's still just the third best player in his class. Shane Larkin was a bad pick. Giannis and Gobert are off the scales good.
To look down the draft at what might've been is too exacting a standard. Every pick in the first five rounds wasn't a bad pick because Brady is the GOAT.
edit: here's a link: http://www.masslive.com/celtics/index.ssf/2018/04/boston_celtics_danny_ainge_gia.html