Not totally following you, but the way you switch from DSX to USX isn’t by turning your arm. It’s actually by changing the way the wrist is moving. You keep the arm stationary, and just move the wrist in a different diagonal direction. Just as an exmple, here’s what that looks like:
Notice that the arm doesn’t change its position, or not that much. But the motion changes. The upstroke escape motion moves from the upper right of the screen to the lower left. The downstroke escape motion moves from the lower right to the upper left. It’s magic!
But again, don’t worry about that too much right now. If you can do either one of these motions on a single string at 150bpm, then you can do it well enough to try it on some musical phrases. See if you can get your hands synchronized on some kind of simple musical phrase that you like, and see what happens. Knowing what it’s supposed to look like is helpful, for sure, so you can occasionally film yourself if you want to check your progress. But these changes between the motions are so slight that you may be able to suss them out by feel over time just by focusing on a feeling of smoothness, good sounding pick attack, and hand synchronization, and keeping in mind generally what is supposed to be happening at a mechanical level.