I'm of the opinion that you can't be too results oriented with trades like this. You simply can't wait and see what the Celtics might get. The future 1st round pick is an asset and I think you have to view it that way. What if that pick could have been packaged in a trade for Kawhi (say Covington, the Kings pick, and some lower asset for Kawhi)?
Would you rather have:
Fultz and Covington or Fultz/Ball/Tatum and Kawhi?
That could be a realistic outcome and, in my opinion, I wouldn't care too much what the Kings pick turns out to be (even if it turns into a great player). The fact that Ainge got that strong of an asset and still got the player he had rated the highest on his board is the reason that Colangelo got fleeced.
I don't think many would argue with Fultz being the pick. The fact that Fultz has so far lived up to the very bottom of his range doesn't mean it was a bad pick. I think the trade is what some people had a problem with.