As far as longevity for extreme right hand usage, I would look no further than the extreme metal crowd.
Guys like Terrance Hobbs (Suffocation) and Bill Steer (Carcass) are in their mid-50s, as I’m sure most of their peers from the OG crew of late 80s/early 90s Death Metal guitarists are, and they are still out there on massive tours all year, and haven’t showed any signs of not being able to hang with their back catalog.
In the shred world, Joe Stump is 64 years old and he’s just as ferocious as I ever remember him sounding.
Between the death metal dudes and someone like Stump, you’ve got RDT, and Stump does forearm rotation, in conjunction with wrist blend and thumb motion.
I think trying to determine what joint motion provides the most longevity is completely anecdotal, unless you did some kind of large study with many sample groups.
Some people have mentioned Morse has a genetic predisposition to arthritis. At the end of the day, thats all it can be, simply. We also don’t know how much background tension Morse had going on. Just because he is a highly proficient player doesn’t mean he might not have had issues with background tension throughout his career.
Also, I’m sure that a lot of players just stop caring to maintain their peak chops as they get older and don’t feel they have much more to prove. Even someone like Yngwie, who I’ve noticed isn’t doing as much vicious alternate picking anymore. Many lines he used to “float” at faster than a 16th note, he’s just doing 16ths now, and he does a lot more pure legato, especially descending. Not criticizing the content of his lines, but a quick viewing of recent live clips shows that he’s not playing like he did in the mid-late 90s anymore (which was when he was at peak nonstop shred shape, around the Seventh Sign through Facing the Animal era).
Combine that with the fact that I’m sure as these players get into their 60s they need to put more effort into their practice to keep their motor control sharp, it could definitely result in sloppier and more tense playing when they do attempt their more difficult material.