Personally, I would pass. If he was free and I was looking for a challenge that I didn't care if I lost money on, I might consider taking him and just seeing what I could do...but the first buck or hint of lameness and he'd be gone. With those legs the way they are (I agree that they weren't caused by him being fat, my guess is that he's a poorly bred halter horse and his legs are simply jacked by genetics), he won't stand up to any sort of hard riding so, as you said, the gaming prospect part of it is ruled out right there. Being a halter horse would also explain the "impeccable ground training".
It's possible that he might eventually be a suitable kid horse, with a few million miles over the next few years (if he physically stands up to it), but it's also possible that he won't. With the age he is, if you take him and put 5 years of work in him trying to make a suitable kid horse and find out he's not...then he's 19 with arthritis, jacked up legs, and a temperament suitable for an experienced rider only. You won't find a buyer for him. At best, you might re-home him for free and be out all the money you spent on him over those 5 years.
Truthfully, I don't think he'd be worth it in the long run. With the market like it is and just coming into winter, it's definitely a buyer's market. For a relative pittance, you can find something that's 2-3-4 years old, maybe green broke, maybe not started, with decent conformation and possibly registered. I/e, something with real potential that has a lot of good years left in them.