His BS posturing aside, the OP's remark that this big 3 isn't good enough is valid. However, I would like to hear an alternate plan that realistically would have us become a contender.
We tried to get one of the top stars in the league in Durant. It didn't happen, but the competition was one of the best teams in the league in GS so it's understandable. Besides Durant, I'm not really sure what amazing superstar was actually available the last few years that we could have acquired. LeBron, Kawhi, Davis, Harden, Westbrook, any of the Warriors stars, these guys were all unavailable.
Ainge did try to get Paul George, but Indiana stupidly turned down our really lucrative offer at the trade deadline. We tried to get Butler but Chicago also stupidly turned us down and ended up with a much worse deal. Also, it's not clear those teams wanted to deal their stars within the conference in the first place. Besides, Hayward is as good or better than Butler, and we got him for free. Doesn't that seem like a much smarter move? Who else was there the last few years? The head case Cousins?
The only thing you could say is, we'd be much better off if the Celtics had drafted Giannis or Jokic. Those are the two superstar potential players who they actually technically could have drafted. Towns, Simmons, Embiid, they were taken before the Celtics picked. Oh, I guess you could say we should have drafted Fultz, if you believe he will become a superstar.