Thanks for posting! What you’re doing here isn’t wrong, per se. It’s just a different motion. This is forearm rotation, and just given the way that works, you will indeed lift the thumb heel off the strings on the upstroke. That’s normal. In fact, if you look at my form in this clip, you’ll see I’m not even touching the strings at all on that side of my hand:
Here’s Doug Aldrich doing this, and his form looks pretty similar to yours:
So basically, there’s nothing wrong with this, and I played this way for literally decades until we started investigating other motions like the wrist stuff. The only concern would be if you can’t play the lines you want to play. Note that forearm motion like this is almost always USX-only, so to get the most out of this you want to make sure and play lines where the final note on the string is an upstroke.
If you do want to learn the wrist-only motions, that’s fine too, of course. One thing that can help is making sure you have no wrist flexion. That’s step 3 in the checklist, the overhead shot:
If you have a guitar with a forearm contour, and you use it, that can place your elbow behind the body. To reach the strings you need to flex the wrist, and there we are. Instead, start with a totally straight wrist and place the anchor points on the strings where want them, while maintaining that perfectly straight line from overhead / player perspective. Allow that straight line and anchor points to dictate where your arm goes, not the other way around.
When your wrist is straight it can be easier to think about moving the wrist without turning the whole arm around. The first step is seeing that it’s happening. The second is noticing by feel when it’s happening. The third step is figuring out how to move your wrist without the arm turning. It might be a little like learning to raise one eyebrow but once you learn to recognize the turning, you’ll be one step closer to learning to do it without that. It just takes a bunch of attempts.
Otherwise, stick with the forearm motion and tool around with it (sophisticated technical term, “tooling around”) to try and get it to go fast while maintaining smoothness. It’s a perfectly capable motion and your form here is close to the way great players do it.