Also, since Africa almost always gets the shaft in this regard, all else being equal, an early African occurrence of something good will be assumed as not definitive, but vague evidence of the non-African first occurrence will be taken more seriously.

Not just in this regard. I’ve seen an integrated recycling project in Africa that was years ahead of anything I’ve heard of in North America, yet people just dismiss it when I describe it. I’ve also visited an African irrigation project where Israeli methods were rejected as too wasteful of water.

Interesting about the leprosy. I’d never really thought about it before, but the impression I’ve had was that leprosy was fairly common so I’m a bit surprised (from a position of almost total ignorance) that it’s not been seen quite frequently in ancient remains.