Ordinary Banana

Yeah, maybe it's hard to improve a relatively well-optimized system that you don't understand with hard-to-control methods.

it would be odd if it were optimized for our comfort and pleasure

Should it be? https://www.huxley.net/ 

it would be odd if things like arthritis and neuropathic pain were for our own good morally

Sure, but pain from arthritis is an indication of autoimmune damage happening.

but what can a human DO about the damage? seems like nature has little reason to spare the rod (or even be reasonable)

Well, there is stuff that can be done, but most doctors would probably disagree with my suggestions....

Anyway, I'm not exactly saying not to take drugs if you have arthritis, I'm contesting your statement that most people should be on drugs.