I'd try a 4' 5" shoot'n stick.....Just duct tape it to the wrist of your bow arm and set it firmly into the ground. You will never drop the bow arm again.
Sorry.........I couldn't help myself.
Truth is, I've threatened to do this to myself just to see what would happen If I didn't drop my bow arm. For me part of this is that I shoot a bow that is not only heavy in draw weight but is heavy to carry. I think that as I release, the recoil and the physical weight of the bow are just too much to keep from falling away a bit.
The guys have offered some good advice. I watched you shoot and you seem to shoot like me. I think one other thing that causes bow dropping, at least for me, is a little target panic.
When it hits me bad, I feel like my bow arm locks on and I can't move it into a better alignment picture no matter how hard I try. Usually I'm a bit high and right of my intended alignment picture and since I can't move my bow arm prior to release, my mind says...."Ok fine just move it as you release"
A guy once told me that when target panic hits, draw your bow, then force yourself to circle the intended spot you want to hit with your arrow point, then align your sight picture and shoot.
Sometimes it works. Good luck