I dont think the stabbing was meant to kill gotti jr, if that was the case he would of been shot. I think it was done to send a message.
That movie , whether it pertains to guys today or 20 years ago is not important. What is important is the fact that a movie about gotti will bring the name Gambino back into the media and im sure none of the guys in brooklyn want that.
Of course this is only speculation, its only a thought.