He may not be reaching under himself as well as the left, but it's hard to tell. I wouldn't be particularly worried since he doesn't look truly uncomfortable. All horses have a stronger side and a weak side, and young horses in particular can be off-balance. Once he gets proper work and muscles up that side I'd guess that he'd be fine, but if the problem gets worse then check for heat and watch him more carefully. You can also have a vet do a flexion test to be sure.
I initially thought the left rear looking like it was trailing a bit, but I think it's an optical illusion since he has that white sock. That looks like a nice floaty trot. Have you ridden him? Might be easier to tell from the saddle.
also, the lady who owns him trims all her horses feet herself. every one of them had vertical cracks and looked awful. he was no exception. he seems a bit flat footed, but has a thick wall, though theyre all cracked. he has no heel height either. is this evident of something chronic even at such a young age?
You'd have to talk to the vet/proper farrier about that, since I'm no hoof expert nor can I see the hooves. It takes about a year for a completely new hoof to grow in. The farrier may get correctional shoeing if needed, which could allow for normal work while the hoof heals. Remember there are also topicals for hoof health that can strengthen the sole, frog, and hoof wall. For the vet check, definitely have him/her take a look at the feet to see the course of action. When I got my first horse, the front hooves didn't have enough heel. I pointed it out to the vet and she said he would do fine with normal work and better shoes as long as we didn't jump for 4 months, just to give you an idea.
I'd be concerned about the left hind. The next step I would take is to put white polos on him, all the way around, to lessen the optical illusion, and look at him/video him again. If having the white at the same level on each leg minimizes or eliminates the visual effect of shortness and/or uneveness, I'd say go ahead.
He is lovely, but I don't think it was the power of suggestion in your thread title - I think I see something behind too.