There is such different types of quarter horses though. At my barn there is a quarter horse that is super downhill. She does dressage on him but maybe just for fun? I know he was started Western though. He’s downhill enough that even my 13-year-old daughter commented on it when she rode him (after only riding quarter horses and ponies herself.) It does look like the horse was trained to just put his head in a frame and not really use himself any differently other than that.
My horse is more of level balance but he definitely can move in a more uphill fashion which is what I personally love about dressage. Using it to improve my horse.
What would be a really interesting experiment that I wish I could do would be to ride the really downhill horse versus my horse or one similar in the same tests. Because the downhill one that I speak of is a bit of a bigger mover than my horse but doesn’t engage as well (and has a bit more of a sour expression.) Just curious how the scores would shake out on that one!
I do follow a very downhill quarter horse on Instagram and I believe the lady even got her bronze medal. You could always tell the horse was more downhill but it did seem like she was teaching it to be at least as a level moving as physically possible. So again it was dressage being used to better the horse.