I have a strong opinion to euthanize this poor guy. I’d bet my next paycheck he has horrible pain somewhere or past trauma and a normal life is not possible. He’s a risk to himself and others.
You’ve seen it for yourself -his behavior, how illogical it is at times and you do reference some known medical issues.
I have a mustang that came TERRIFIED of my zero turn, my tractor, cars pulling up, the sound of metal clanging, the wash stall, clippers etc etc etc. All normal for someone who for the first 6 yrs of his life did not experience any of it and is a flight animal.
But today, this guy might still raise his head as I’m coming towards him with machinery but that’s it. He knows he’s safe. We’ve worked through so much and now the plan is to haul to a horseshow this spring. Just to graze, relax and go home. Because it might be a big deal to have all kinds of comotion and he won’t be used to that. Right?
The pain he DID feel - FEC 2100, molar extracation, root canal on an incissor found through fistula in his gum and then xrays is all gone. I’m sure that has all helped EVERYTHING. He’s relaxed and quite the adorable pony and coming along nicely under saddle.
I didn’t see how long you’ve had him but any horse that is able (mentally and physically) will make progress with training. You have a lot of experience. If your gut is telling you this is very wrong - listen to your gut.