Disagree. I find that the off hand is often the key to fixing poor shooting. In an ideal world, the off hand should not even touch the ball. The only purpose it should serve is to balance and stabilize the ball in fast paced game situations. Using a missile analogy, the off hand is the stabilizer, the shooting hand is the guidance system and the base and legs provide the thrust. All of these must be coordinated and synchronized in order to achieve a consistent and effective jump shot. Most great shooters will tell you that when they practice the basic fundamentals of their shot, they shoot the ball one handed and the off hand does not even touch the ball. In this picture you can see that the off hand is actually placed behind the ball rather than on the side to gently balance the ball. Given its placement, the off hand on this shot will have a significant detrimental impact and interfere with the rotation and trajectory of the shot. I will also add that I find the way he places his shooting hand on the ball to be problematic. The palm should not be laying flat on the ball. This leads to a poor feel for the ball and ends up in shooters pushing their shot. The ball should lay on his fingers with a gap between the ball and his palm. This results in a cleaner release and better rotation on the ball.
The off hand can do anything it wants provided it doesn't transition from balance/stabilizer to any part of the guidance or thrust. Maybe that's what you were saying.
The ideal release in a jump shot has no element of a push to it. Keep the elbow/arm out of the thrust. Extend the shooting hand to its highest point and practice releasing the ball with the wrist. With the palm facing the floor at completion. That gives you the best trajectory and most consistent/repeatable guidance and thrust.
Your palm talk is spot on. One other item. Verticality throughout the sequence you describe is critical. Shurna did not maintain good verticality with his shooting elbow and arm. His was not a push shot. His wrist release was really good. The flat trajectory came from a relatively flat lack of verticality in his release point.
I had great fun teaching kids to shoot. The first thing they learned, no matter the age, was lower body thrust, a sense of straight up verticality to everything they did and hand under placement to promote the critically important wrist flip finish. Getting the off hand out of the wrong sequences was the most common challenge among the younger ones. With age and strength they could mature to a continuously higher release point and add in the jump if and when they could.
BTW ... in my experience breaking fundamentally bad shooting habits/form is nearly impossible from about the 10th grade on for anybody who has played quite a bit of basketball. You can tweak, but the full body off restoration is really tough.
GOUNUII