Ordinary Banana

like wouldn't you think with all that pharma tech, thousands of compounds, only extreme outliers wouldn't benefit from any of them?

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....