With all that said if Tatum wanted JB to still be on this team he would be.
This kind of statement gets thrown around a lot. It is a hypothetical, so no one can say for sure either way. Tatum has said in the past, very clearly, that he does not want to get involved with personnel decisions. He does not want to pick his teammates. I believe him.
As to the premise, did Tatum want Jrue Holiday off the team (for example)? Would they have not traded Holiday if Tatum said not to? How about Porzingis? Or does this idea of veto power for Tatum only apply to Brown?
I don't buy the logic that they would not have traded Brown if Tatum didn't want him traded. Or that because he was traded, it proves that Tatum wanted him traded. It could be true that Tatum was ready to move on from Brown, I have no way to know that, but that is different than assuming Tatum had any influence on him being traded or not.
Remember, the first try was to trade him for Giannis. Who wouldn't want to trade Brown for Giannis. After that fell through, I think it would have been tough to keep Brown around no matter how Tatum felt about him.