So I will offer an alternative point of view. A trainer I highly respect told me that the horse’s mind and work ethic will go a long way towards performance and mitigating conformational flaws. If anyone argues against this, then dressage has become a 1000-lb poodle show and not a test of training. Which is something we are currently debating.
As far as sickle hocks and “dropped” croup, those are features that this trainer I repect valued as they were signs of a conformation that allowed the horse to easily “sit” behind.
I do see and very out-of-shape horse that has no muscle. I don’t see any limits to what this horse can do just from the pictures.
What I recommend is to put the horse in a small enclosed space, preferably with corners, and do a free school. Ask the horse to move on. See if it offers trot or canter. See if it naturally moves into a canter when you ask for more. Ask for a change of direction. See if the horse can sit and do a balanced “roll back” to change direction when it gets into a corner…or see if it falls on the forehand, breaks into a trot and makes a big circle into the new direction.
Seeing the horse in motion, at liberty, will tell you more about what nature has endowed it with than a still picture from a bad angle.