What were the exact findings on the neck X-rays? With so much front end involvement it may not be his back at all as the main concern. Did a specialist measure the distance of the spinal canal or note any narrowing? Was just talking about this with someone this week. Comparing two cases of “wobblers” in the past month. (Quotes because compression that’s not early development isn’t exactly wobblers syndrome right?). One was a 5yo WB that had a couple questionable events, grew a lot, then became ataxic pretty quickly. The other was a 14 yo GP dressage horse who’d always been a little weird but you know, was showing at GP. Did have that freaky front end movement. Pretty suddenly had trouble just getting around. I’ve also talked on here about a horse I worked with who also got neuro at 14. He had ECVM and a LOT of arthritis. I think it was the arthritis that contributed to the impingement in his case though I never saw the report from when he went to NBC.
If it really is neck and neuro, then none of the rest of it really matters as far as management and prognosis. I’m with your vet on that. Although if his back hurts or he’s lame or his feet are long or sore, he might avoid certain behaviors due to discomfort or feeling unsafe dealing with that with sub-optimal proprioception.