Idk, Don's behavior on the court changed dramatically after Joe left. He became a black hole on offense, especially at the end of games where he became the worst clutch player in the league by a mile. No way to know how much was Joe's influence, but it sure is interesting we see a true change on the court after we trade Joe, even when he hadn't been playing for a while due to his injury and the play hadn't really changed that much until he was actually traded. Then the blender stopped, and the end of game melt-downs became not just more frequent but damn near inevitable. If Joe were a solid locker-room presence, for whatever reason, then what we saw on the court sure makes sense in that context when he left.
Point is there is actual tangible documented and data-driven evidence as to a change in the team and DM's play. Now whether it is causation or correlation is fully up to debate, since we weren't in the locker room. But guys like Jones, even if he is just a glorified fan, had access we did not. So even if he is spinning this nicely, it still is pretty damning and fully fits the evidence available to us.