no it is not overreaction at all. It is actionable slander. Infact since it has to do with professional reputation it is slander PER SE!!!
It's a ridiculous over-reaction to think that anything Dr. J might say would ruin Danny Ainge's pristine reputation as a man who never lies, killing potential trades he had on the table.
Arguably, Erving just accused Celtics and Lakers management over the years of just doing their jobs and trying to "win" trades. So long as he's not accusing anyone of actual criminal acts, I don't really see the problem.
Are you going to suggest that KG should sue anyone who calls him a dirty player because you think it might cause him to gain a reputation as a dirty player that influences refs to call more fouls against him?
This is just part of the game and part of life. While there may be a case that the league office should issue some form of sanction, suing is just a stupid idea.