This is an interesting perspective, and I have an easier time following your line of thinking when you lay it out this way.
I do think, in general, it’s abusive to a horse to ask it to go around a 1.2m course with a rider who repeatedly puts it in a BAD spot before a jump, gets left behind over a jump and hits it in the mouth, and fails to do anything even remotely resembling balancing the horse when going around turns. All of those things happen A LOT in the jumping phase of modern pentathlon.
I’m not sure just lowering the jumps will help though. In fact… it might even make matters worse in terms of uneducated rough riding.
At the end of the day, I do think the responsibility to not put a good horse in this sort of situation is the responsibility of the horse’s owner and the riders. I disagree that the focus should be on the coach in this situation, as much as it is. But we can agree to disagree on that one
Maybe lowering the jumps a bit, and changing the nature of the jumping test to something more like a handy hunter round would eliminate some of riding issues that bothered me most when watching this unfold. They could do some larger jumps, but also would have to demonstrate other riding competency and control while on course.
Or, as I said earlier… just have these folks do motocross instead in this phase.