Nice balanced horse with a few faults.
This is what is wrong with horse breeding and why we have such 'fragile horses' that are born just looking for a place to die or a reason to become crippled.
We have bred horses for the kind of conformation we want or need for the purpose we want to 'use' them for. 'Mother Nature' has bred them to survive. So, everything we find 'wrong' with them is usually exactly what is 'right' for a horse to remain healthy and sound and survive under extreme conditions. They just do not 'fit' the mold we have made for the horses we want to ride.
We have bred horses that are waaay too refined and 'pretty', waaay too fast and waaaay too fragile. Then we stick them in stalls or little pens and feed them waaay too much. [Probably the worst fault I see in this mustang is that he is over-fed and too fat.] We are now paying the price for such fragility and over-feeding with high Vet bills and a high mortality rate.
What you are looking at in this horse is a perfect example of 'survival of the fittest' -- only with a prettier head than most of them come blessed with.