The other side of that is that, given the long time COVID takes to kill someone and the amount of time they are infectious before that, it doesn't have much of a reason to become less deadly. Sure, it could mutate by chance to become more benign, but if it's communicable for twoish weeks, including while asymptomatic, then stops being communicable, and then kills the host what does it matter evolutionarily speaking that the host died? I don't think there's any pressure on COVID to become less deadly.