A lot of mustangs have low tying necks and big feet. Those are things that have been selectively bred out or culled against in many breeds because those traits are considered either not "pretty," or not functional.
I am not being mean here, so please don't take offense, but... He does not have a short back. Nor does the dun horse in the profile picture. He is somewhat long over his back, but he has a good shoulder. I really can't say much for his hip because he is standing a bit awkwardly on his back end and isn't square, so there is no way to make an accurate determination there. A lot of people criticize horses for being long, but long isn't necessarily bad. Balance is what is really important. If you broke the horse apart into three pieces - shoulder, back, and hip - you would want all those pieces to be as close to equal in length as possible. It's okay for a horse with a big, long shoulder and a big, long hip to be a little longer in the middle than a smaller, shorter coupled horse. Most western performance horses are actually pretty long-built. In keeping with balance, you want the horse to have a shorter topline (wither to hip) compared to a longer underline (armpit to flank). He actually has one of the better shoulders I have seen on a mustang, which is a good thing because a longer, more laid back shoulder typically indicates a smoother ride. I really think he's a nicer made horse than those duns you are comparing him to. I hope he's a good fit for you.
