[Nevermark]

I think we are more or less agreeing, but emphasizing different valid sides.

After all, as much as cross over illnesses are orders of magnitude more dangerous, they are also orders of magnitude reduced in threat distribution, for any low population species.

The integrated surface x time surface area for transfer just isn't there. Lots of low population species last millions of years, or tens. And even then, die off for other reasons. despite their extreme and persistent low-diversity vulnerability to any successful cross over parasite/illness. Neanderthals are not exceptional on that count.

To be clear, I am agreeing with you (and me!).