It could be part conformation. He is straighter behind with a steeper croup.
I don’t believe his trot is correct. I don’t want to see that level of tension in a sport horse. You occasionally see this movement on the track, which is why it’s called “being tracky” - where the hind end is snappy and horse moves like a pogo stick with a locked back. Usually caused by combination of factors - SI soreness, management, and sometimes undiagnosed injuries brewing.
But his back is stiff with very little movement to it. These horses are hard to ride.
The difference in range of motion from left to right, stiffness in his back, inconsistency, tension, lack of tracking up, and the way he’s holding his tail would make me, as a potential breeder, want to see him in a well-proven sport career before I considered him for any mare. These are overlapping symptoms of several myopathies and neurological disorders, so I would want to see him with an established career first.