One thing I noticed is how early your arm is cocked when you are in windup. It’s not just starting to cock early–It’s fully vertical before any part of your stride foot is in contact with the ground. The video you have from stretch cuts off your arm, so I can’t tell if it’s the same situation.
Generally, having the arm up early (rushing) results in decreased arm speed at release because the arm is in pause mode until the lower half catches up. Hence the term rushing the arm.
You seem to have a strong front side, stabilize well on the front leg, and finish up and over the stride leg with good rotational energy for the upper half. The rushing is sapping your velocity.
Another thing that may help you maintain early balance through your leg lift would be starting with your pivot foot turned slightly away from the rubber. The turning and twisting you do during your lift, may trigger early hand break as a way to maintain balance. You really don’t want to be rotational over the rubber. If you start with that foot turned slightly forward (and don’t reset it during your step with the free foot–leave it angled), you won’t be able to twist as much to the rear and it may allow you to keep your hands together at least until your hip can begin to thrust forward. Also, if you can take your free foot even slightly behind the rubber during your step, it may help you generate earlier forward momentum and reduce the early rotational component that may be effecting your timing. Right now you step to the side if at all–which wouldn’t kill you if you didn’t have that Luis Tiant thing going on.
There are two ways to get your front hip forward: 1) thrust it out at the top of the lift with a slight movement back with the front foot at the same time you drive out with the pivot leg. 2) get your knee up and forward of the rubber as you begin the lift which will preset your front hip and rear leg angle.
The second way is easier to keep balance and delay the hand break. It’s more similar to stretch position leg action except done from the wind up. This is also why, in most cases, rushing is not as severe from the stretch.