I am not sure San Antonio would be willing to give up Dylan Harper or Stephon Castle for Giannis. Already 31. Regular injuries at this point.
I think the Spurs will take the long term view and believe they will win more in the long run with these young guys than they do with Giannis.
I'd also wonder about Giannis hurting Wemby. Taking Wemby out of his prime touches / locations. Relegating Wemby to 2nd option. Harming his development.