Anabel, I think what you say makes sense, and it has triggered a bit of thought on my own horse, Cinny. He is a Paint, with a missing vertabrae, stiff sacroilliac and was born a tad over in the front knees. True he didn't start work until age 8, but am I pushing him too hard into something that is too hard for him? Maybe I am. Should I lower my expectations, maybe I should, or at least re-evaluate them and try different things.
Do I think another discipline would be better for him? Not really. Going over jumps would make his fore break down even faster and put more pressure on his sacroilliac and back. He's not suited for WP at all and would take a big effort on his part, even more than dressage. Barrels, reining...again, the front would break down too fast. He's probably best suited to be an every day trail horse. But, again lower level dressage would most likely strengthen the muscles where he has problems and at least build him up to help him use his body more effectively. Anything beyond training level is probably too much of a push...which I have already concluded a long time ago. Western Dressage where he doesn't have to stride and float AS MUCH, might be better for him.
Does this make sense to anybody out there? And thank you Anabel for promoting more thoughtful thinking where it comes to my horse's future. Sorry to temporarily steal the thread.