Umm... many top jumpers start out in the hunter ring. Hunters are not about being pretty. They are about being correct. You can't go blast around a jumper course safely without having those key buttons put on your horse. Stride control, even pace, correct spots etc. I have actually seen many riders get kicked out of the jumper ring because they were not safe.
All my event horses start out in the hunter ring. I want a horse that I can take out and know all the buttons for stride control and distance are there before I hit up a timed jumper class or take my horse out cross country.
And again, the reason position is so important is because it helps your horse perform to the best of its ability. Correct form is about keeping your horse happy and healthy.
I've ridden with a few jumper coaches that send horses to a dressage trainer before they even look at a pole. That dressage training is very helpful in the jumper ring. Those correct roll backs are hard to ride if the horse doesn't have the proper foundations on it.