I doubt it makes much difference who is available at #3 to whichever team is going to get it.
The early timing of this deal before the draft is a strong indication there will be another trade before the draft. Most think it will be Butler, but George and AD are also possible.
Another factor is Ainge may not want to take on any more 19yo hotshots who require 2-3 years development. Most of the lottery picks these days are 19yo. I just read an article by Kareem Jabbar decrying the system whereby these "6 months and gone" kids play a few games in college and then go into the NBA draft.
I think Ainge wants to win now. It's been 9 years. And he needs a veteran star or two to get to the next level.