Strop seems taut enough from the vid. It is hard to tell but it sounds to me like your pressing too hard. I may be wrong. You need to keep the spine on the strop but you needn't apply more pressure than it takes to do that. If you watch the video you will see that you are stropping heel to point on the stroke going towards you but you are missing the point end of the razor completely going away.

IME if you hold the tang further out on your index finger towards the tip it might make the flip and the tactile feel of feedback better. YMMV. I found that when I began to strop with the tips of my index finger and thumb I was better able to control how much pressure I apply to the edge. Again, YMMV, everyone sort of adapts their own thing as they learn. I think your wrist is fine.

The only other thing is also personal preference. The old barbers hooked their strops on a hook on the arm of their barber chairs. The strop was usually level of slightly higher at the hand end than at the hook. I stop attached to a door knob to achieve that relationship. A lot of guy strop 'uphill' hooked to a towel rack but I wouldn't be comfortable with it.