Good videos thanks. always makes it easier to see from two angles. there's some good stuff there.
See Imgur file here - http://i.imgur.com/2UYgx46.jpg
firstly you're rounding - see video for quick explanation - try keeping your hand out further from your body - Barry Schultz has a massively exaggerated form for this. https://www.youtube.com/watch?v=7GaDG7aX5A8 to break bad habits I woul dsuggest trying to reach out as far as he does to being with.
secondly your hand is leading the disc instead of staying on the outside and utilising the pivot. by staying on the outside longer it should actually correct a number of the other issues (elbow will get further forward, should pull the rounding in slightly)
Best drill to sort both these issues is this - https://www.youtube.com/watch?v=LffYBb1vQjQ you can skip the first 4 minutes.
On the reachback - you do physically reach back and this takes you out of posture (head outside of your feet) SW22 has done a superb series of videos and drills on this issue - I have made a playlist here showing them all in a good order to work on - power of posture is a great video https://www.youtube.com/playlist?list=PL_9kf03fmbhXpwZJ-f7SDIOUyIb_eF-Om Door frame drills are good for the idea of working around the disc instead of reaching back. (the disc almost stays in the same position as you fold and unfold around it.)
You get horse stanced as JR mentions your front toes are pointing almost to the target - this is a powerful martial arts position, it is not a dynamic disc golf position - again SW22's videos cover this well but try to shorten that stride and keep everything more compact and upright, keep your upper body within the confines of your knees. Don't lean out backwards or rock forwards of your knees or you leak power.
You do seem to lead with your hips well and engage them surprisingly well considering the horse stance, this is good and will make life easier for you later.
by working on just the closed shoulder drill to begin with you should see a huge increase in accuracy and easy power along with it although distance may not improve greatly, work on the posture stuff later. The closed shoulder snap drill should help you make the disc do the work for you. At the moment you are trying to force it on its way (hadn leading the disc) utilise the pivot and you can let it help itself!