Mitchell is clearly a very, very good player. He's probably not going to be a generational talent, but at the age of 24 any team in the league would immediately insert him into the starting lineup and become significantly better. Several already good teams would become instant contenders if they added DM to their roster.
So why on earth does Shaq need to go after a young guy on TV just moments after he had a really good game? Was Mitchell bragging about his skills, or otherwise claiming to be something he was not? Did he need to be taken down a notch for some reason? What did DM do to deserve the treatment he got, getting called out by one of the legends of the game in an awkward way designed to humiliate him.
This was not about Mitchell, it was about Shaq being a major jerk.