I'd still do the deal, and I think he will be an excellent offensive player in a few years. He makes good decisions, passes very well, and will be tough to keep out of the lane. He can take contact and finish. Next year, he'll start to show more, and by the time he's 22, he'll be producing consistent offense.
I don't doubt that Spoelstra is a good coach, but Stevens would have made more out of Winslow by now. Stevens is better at figuring out what players are good at and setting up roles than any coach I've ever seen.
If we had him, Crowder would still start and play normal minutes. Turner and Jerebko would lose the minutes, not Crowder. We would play more small ball and have a terrifying defense. It might hurt us a bit this year because Turner is playing so well, but in the longer term, Winslow would be perfect for us without diminishing Crowder. Both guys can play 3 or 4.