The jury is still out on the virulence of omicron. Perhaps we'll get lucky and, that despite likely immune evasion, omicron will have a low clinical impact, even as it may infect many.

A virus that may have developed multiple mutations through infection of an immune-compromised host over many months would likely have killed that patient were it severely virulent.

I am not aware of too many infectious disease that spare the immune compromised and ravage the larger healthy population. Inverse natural selection (deselection?, unnatural selection?) is not a likely outcome.

Mutation has undeniably occurred.

Time will tell if natural selection favors Delta.

Fingers crossed that omicron proves as inconsequential as Epsilon, Zeta, Eta, Theta, Iota, Kappa, Lambda and Mu (this list courtesy of wikipedia, not google).