Native americans had like a 95% population mortality rate from infectious diseases in the first generation of European settlement, no? Measles, smallpox, flu, etc.

The mortality rate from those diseases was higher than today because the population had no immunity at all, leading to both higher transmission rates and higher mortality rates. This would be true of an engineered virus as well.

And it wasn't just the one virus, it was an entire continent's infectious disease arsenal landing in overlapping waves. Again, something you'd do if you were trying to maximize damage.

So I don't find the bulk of the article about it being impossible for a virus to have this effect all that compelling.