First of all, this was a terrible trade for the Mavs. They are trading a future MVP, who is only 25-years-old, for a 31-year-old player who is about 70% or less of his peak, and a first round pick that won't even lottery pick.
I in no way believe that this was the best deal they could get for Doncic. Other teams would have offered more.
And this went from a team that went to the finals last year, to a team that is rebuilding and won't be in the playoffs for years.