SGA was the 11th pick. Typically with top 3 picks you know almost immediately if they are going to be good or bust out. Just how good a little less known (Sarr is a good example of this), but there are very few guys that go top 3 that start off really poorly and then hit (even Brown by year 2 it was obvious he had real talent) or start off really well and then don't get better (Ben Simmons says hi). It does happen, but it is rare. For the most part almost immediately you have a real idea on if the guy has it or not when they are top 3 picks.
Being able to determine if a prospect is going to be good and having that prospect actually be good are two different things. I don't disagree that in many cases, you can see right away if a player has NBA stuff or not, but not always. But even SGA, teams saw that he was going to be good but it still took several seasons before he was actually that good. It was 5 seasons with SGA on the team before OKC had a winning season.
It makes no sense to me to trade a bonafide All-NBA level player in his prime for a 19 year old rookie unless you are in full re-build mode. At best, it will be 3 years, and maybe never, before Dybantsa is better than Brown. How does that help BOS win a title during Tatum's window?
SGA's 1st season in OKC they were 44-28. They lost a 7 game series to the Rockets losing game 7 in Houston by 2 points. They tanked the next 2 years in part because SGA got hurt the 1st of those 2 years. They won 40 in his 4th year and haven't been below 57 since.
SGA is one of the best players of this generation, and he didn't get a team out of first round of the playoffs until his 6th season in the NBA, correct? Sure, he had injuries, or was that all just part of the tank. The team clearly did not think they could win with him or they would not have continued to tank for all those seasons.
We are going back and forth on this but I do not believe that Dybantsa will help Tatum win a title over the next 3 seasons more than Brown will. That is the position that you appear to disagree with. Brown is a Bonafide all NBA player in his prime. Dybansta will be a very promising 19 year old rookie. So if the objective is to put the best team around Tatum, with the best chance to win a title in the next 3 seasons, then you do not trade Brown for a rookie.
Now you have also suggested Brown + #27 for Young + #1 (Dybantsa), that to me is at least worth discussion (even though WAS probably never does it). Young can help Tatum win now. Others have said that they would rather have Dybantsa for the next 12 years (or whatever) over Brown for the next 4. That will probably be the case IF Dybantsa actually fulfills his promise (not a given), but where does that leave the team for the next 3 seasons? I am guessing that Tatum would rather trade Brown for Giannis or not trade him at all over tading him for a rookie.