Here is what I see. A QB is the team leader. Leaders put the team before themselves. I don't fault him and I think the argument that the offense is going to value a different skill set is valid. He is too much of a talent to be a benchwarmer. While these things can be acknowledged, his response to Fields was not consistent with leadership. Frustration, disappointment, a naive attempt to exert pressure on the coaches, youth...these things may explain his reactions and all are understandable. However, Martell has communicated fear, not leadership. He has communicated that it is all about him, not the team. He has every right to do that, but I hope that he realizes that such attitudes and behaviors disqualify him from leadership.
By entering that portal, Martell told his coaches and entire team that it's his way or he will not be the QB next year. When he took this step, he ensured that it will not be his way. I have not seen any evidence that this kid is the promised one, but I really hoped he might be until his current behavior. Now, if he leaves, I can only wish him the best.