I’m sorry if this is going to come across the wrong way… it sounds like you are saying that you will not try a different farrier/barefoot trimmer because your barn owner/trainer will not allow another farrier/trimmer to work at her/his barn.
Let me just say that I have experienced this at a barn and it sucks. Not only did my mare not need shoes at all, but when I was pressured by the barn owner to shoe her she went downhill fast. It took 2 years to bring her back from the damage that farrier did. Now we are competing happily and successfully barefoot in lower level dressage.
Your situation is different because you have a diagnosis, but you also said your horse was better without shoes.
You are your horse’s advocate. You must make the best decision for him, not the barn owner, trainer or farrier… YOU
It sounds like perhaps a different barn that allow owners to make their own horse care decisions is on order… ASAP