Curious on this chart thing. Can /sci/ confirm or deny this?

I've heard that many deadly viruses like that one in india aren't really a threat because it has trouble spreading, and I've also heard that a lot of pandemics of the past ended because the virus mutated into a non-threat.

However I also heard that viruses need to spread to be able to mutate, which is why its important to watch those deadly ones that dont spread easily to make sure it doesnt mutate into a variant a lot more transmissible but only slightly less deadly.