Yes, this. I knew someone who had a horse with navicular (similar degenerative condition of the foot bones), and he was a great fit for her as a part time 'plod around' pony. They can be fantastic for the right home, if it's not so bad that they're unsound in the paddock. Keep them comfortable, they get to live fat and happy, and every now and again have a grandkid plonked on them for pony rides or you go for a slow plod down the road together on sunny days. I don't know if this guy would be unsuitable for a beginner- they say he needs medication before and after rides and 'acts up' without it. They might be asking far too much of him and he's just in pain. If he was giving littles pony rides, or they were staying within his capabilities, he might be a perfectly good beginner's horse- a paddock ornament with weekend strolls might be his perfect home.