The "down-slam" of the bow arm is unlikely to be related to tiller, grip configuration, or your body-draw geometry. It appears that you have poor follow through and have developed a bad habit of dropping the arm to watch the arrow flight. At least as a training aid, I would recommend using a wrist sling and relaxing your grip. Practice your form at very short distances and intentionally follow through for several seconds. You might even want to practice this with your eyes closed. It might take a long time to break the habit. There is not enough detail to see consistency in your anchor and release. You do release very quickly. When practicing your form with bale shooting, I would also recommend delaying your release by at least 1-2 seconds. Everyone I know who has been successful in slowing down the release has seen a big improvement in accuracy and consistency. I am now in the 3-5 second range and doing better than ever. Of course, that will be difficult if you are overbowed.
Best of success.