Yeah - I didn't want to insult him ;~D
Look at how muscled her shoulder is compared to her butt. He's at least relatively proportionate.
She looks like she's been pulling a cart for a living.... or... I bet her trouble is that she is really heavy on the forehand and just lets her rear follow along.... no one has ever asked her to engage her rear or do any collected work.
That's it. That's what was bugging me. Her front doesn't look like it belongs with her back. It wasn't that she was thin in the butt that I was seeing but like the two didn't go together.
It also looks like that mare is standing on an incline, and they really didn't do a good job of posing her for the picture. Her neck is really thin, though, and her head is a bit big. But if they got her standing correctly, we might see a different horse.