More challenging too because most stock horses aren’t going to be over 16 hands. It doesn’t mean they don’t exist or you can’t find them, but it does make it harder when you are looking for a certain height.
I would worry less about bloodlines, and focus more on how the horse is put together and how the horse moves.
ANY horse can have a soundness problem – even ones with perfect functional conformation.
I had a real nice Quarter Horse a couple years ago that I rode for a few months to tune up for my aunt, so she could sell him. While I’m more of a western person myself, I do like to dabble a bit in English. This was him; I thought he was a looker! He had nice conformation (here) and well balanced. His pedigree (here) wasn’t super fancy but I’ve had several Two Eyed Jack horses in the past and they have always been nice horses. Just good foundation-type breeding.
I actually sold him to a client of my English trainer. My trainer had ridden him for her and she just loved him. She thought he had all the different gaits and the suspension needed for dressage. His new owner has since passed away (cancer) but my trainer still has him. And I get to see him from time to time.
He was about 15.2 hands or slightly under.