Here is my view on this..
Do YOU like the horse? If so, then go for it. Don't bother with other people's opinions. Everyone will point out something that they don't like. That's why they have so many different types and sizes of horses. To each their own. I can see he has powerful legs.. and I think with enough training, he can build up his back a bit. It may be a funny angle.. but the second picture makes his back look a little warped.
Either way.. if you feel he could right for you.. then go for it. Only you will really know what's right or wrong. Good luck!