I still can’t quite tell from the new videos, but I think your main problem is that you’re simply not clearing the strings all the time when you try to make changes. Maybe someone with sharper eyes and ears than me has thoughts here?
Another possiblity is that you’re doing some unintended muting with part of your thumb, finger or hand that is causing to pick attack to not produce a cleaner sound.
Yet another possibility is that the synchronization with the fretting hand is not quite there, and notes are getting “choked out” a bit due to lack of synchronization.
One simple test would be to just tremolo pick a single note and see how it sounds. If you’re happy with that, move on to test a six-note pattern on one string, and see how that sounds. If you’re happy with that, try a test where you move a six-note pattern across the strings, one adjacent string at a time. The point is to figure out whether the thing you don’t like in your picking is still present in the simpler tests, or if it only arises in more complex things.
Posting videos of those tests should help give us clearer evidence of where your difficulties are coming from.
Or maybe this is something @Troy has encountered a thousand times before, and he can diagnose you just by faintly hearing your playing through a wall.
Since your wrist movement seems very fast and smooth, to me, if the problem is that you’re not actually clearing the strings, the solution would be to change your arm position to produce a steeper pickslant; in the case of UWPS, this would mean having the forearm rotated slightly more inward (pronation direction) so that your wrist-oriented UWPS downstrokes lift “away” from the guitar more. This might result in your wrist having a slightly more extended bend in it, but it should still be manageable.
Conversely, you could try to take the wrist-based picking technique you have and use it for DWPS by rotating the forearm slightly more outward (supination direction).
The goal is to ensure that pickstrokes in one direction (upstrokes in DWPS, or downstrokes in UWPS) escape the plane of the strings without hitting any unintended strings on their way out.
If you have strong evidence that you’re already clearing the strings, but the sound isn’t to your liking, then it makes sense to experiement with changing the orientation of the pick itself to get things to sound the way you want, which could include something as drastic as changing how you hold the pick.