The mortality is relatively low and mostly affects weaker people already, not that they deserve that however.
The biggest issues so far is how well it spreads (high infection rate), how debilitating it apparently is, despite not killing (high hospitalisation rate) and that governments reacted inadequately, leading to a severe impact on the world economy
For me, the diseases that can classify as a 10 would need to have a high body count (in small amount of time), high infection rate preferably as well, and huge societal impact
Black Death, Spanish Flu, Smallpox (especially in the New World) are solid contenders
HIV is high on the list, but not a 10.
Covid has a chance to get to a 10, but it would need for governments to really half-ass everything
So far the US is the country I'm most worried about>Well developed infrastructure allows for extremely rapid spread>Top level goverment actively does fuck all>Very invididualistic populace means goverment measures might be taken less seriously