As far as the move and the reasons for it. I don't think Ainge saw it as a gamble, he wanted to pick a different guy. I suppose every draft pick is a gamble of a sort for every GM.
Ainge clearly, didn't care for Fultz. Trading out of the #1 did two things.
It got him another far off #1 pick that perhaps, he didn't have an immediate need for except to perhaps, trade it.
Maybe, Ainge thought the reduced the cap impact of the #3 or lower player picked this week was more important than getting another guard.
I don't think it will damage his legacy. His legacy is about winning another title and he has already proven, knows how.
If the endless string of "OMG the Lakers are good!" and "OMG the Lakers are bad!" threads are the price we have to pay for this move by Ainge? I'll take it.