All viruses attenuate. Evolution is a word for it. It is studied apparently by “Evolutionary Biologists” seems to me that’s about where the similarities end. But I keep coming back to that “gain of Function”” thing. If this bug got a “boost” on the way to becoming a Super Bug seems it could lose that pretty quickly.
Any mutated characteristic that encourages lethality costs the organism the ability to proliferate as widely as possible. Maximized lethality is a potential evolutionary dead end. Best case for a virus every host gets infected no one dies.