I actually have the opposite problem, I've got too much roll sometimes, sounds weird but trust me it happens and I get roll out because of it.

I noticed that when you throw (from your previous video) your wrist is cupped to full mast.  I think you're not relaxing your wrist early enough so beacause of that when you are letting go of the ball all of the weight is on your thumb and in your thumb hole so you're not able to let go of the thumb to lift through the fingers properly.  As you lean down for your release gently roll out your wrist and release your thumb, a small roll will begin and finish the rest with your fingers.

Using your wrist the throw the ball will create a lot of revs but kill your entry angle and prevent you from being able to consistently hit a target because now your whole arm is determining where the ball goes instead of being able to follow throw with your target using your hand.

Just my two cents! I'm working on the same things right now and it's been getting progressively better.  Just remember that if your thumb is still facing up in the air just before your release then you're over-cupping the ball.