I don’t know anything about this trainer at all, so I am not doubting what you say about him and the quality of his training, but that kind of sensitivity is one of the things Iberian breeds are known and loved for. However, it is a double-edged sword and exacerbates their tendency to go tight in the back and at the poll. It’s something you have to be conscientious about if you’re training a PRE or PSL. They can look “correct” in their shape without being through. They will react with speed and precision and be overachievers all day long - but to get them to do it with softness and come through the back takes attentive work!
What I am seeing in the Gabiel video that looks like tension to me is (1) The tempo in the piaffe appears quicker than in the backwards piaffe and passage, which gives the impression that he’s snatching his hind legs up rather than engaging his whole body in the full gymanstics of the movement. This may be an optical illusion? But it’s having an impact on my view nonetheless. (2) The poll and throatlatch area look completely fixed, with the neck compressed at the throatlatch - there’s very little motion there during the movement. There should be some undulation in motion with the gait, especially as he goes forward in the transition. That would indicate a greater degree of throughness.
It’s harder to describe what I’m seeing that looks like tension in the back, but that too is about stillness where there should be motion, or maybe some disparity between the movement behind the shoulders (less mobile) vs. the haunches (more mobile).
Some examples that show motion at the top of the neck and give more of an impression of throughness (to me):
- This horse is even actually spooking in this environment, but is softer in the poll and less compressed in the neck: https://youtu.be/kE9k6WXGOpQ?t=189
- https://youtu.be/VuoA40RLNJA?t=17
- The first few seconds of this clip show the neck, though this may be a bad example of it
https://youtu.be/ZaWsKg7C0VE?t=24
-
https://youtu.be/3vOYT1mC8HM?t=255
(He does a piaffe in the pillars, turns around and does another the opposite way - both are difficult to see)
All of these also show about the same tempo, and there’s an impression of “ease” in the movement, even with the spooking horse. I could certainly pick apart other details, but the purpose of sharing these videos is to show examples of what I was not seeing in the Gabriel video.