I agree that they were built for pulling, but I think the mind of the horse has just as much to do with what a horse will be good at. I have known horses breed and built for jumping that did not like doing so. They were much happier with another occupation. I think everyone has heard of the horse that some cowboy is just giving away, because despite the cow horse breeding, the horse hates cows. The shire that I talked about earlier foxhunted into his old age and he loved his job.
Right, I agree - heart has allot to do with it, but regardless of heart, if the horse doesn't have the correct conformation to do the job, the horse wont beable to do the job for long, or has to stay at a certain point to prevent from breaking down.
Drafts bones are not the same as a TB's bones *I just use the TB as example* nor are their joints the same as a QH's. Their bodies mature slower, their pasturns are shorter, their shoulders, their hips - a draft cannot take the traction, impact, trauma as well as horses who are bread for that sport can.
Now, granted - there are horses out there who aren't drafts that don't have the correct conformation either and there are many out there that break down because their owners are in it for themselves and not their horses - but drafts aren't bred to be jumpers, they are bred to be work horses.
Yes, there are beautiful and well bred Draft X TB's. Because they are bred properly, carefully. Same with other breeds that are bred with the mindset of tough compeition.
I am not arguing the fact that drafts can jump. I see it, I've seen it, I've ridden them. What I am saying, is that they will and can break down before they should, because their bodies wont permit too much of it due to how they are structurally, physically made.