You have a fundamental error - the virus doesn't try to "optimize" or "do better". It's pure luck, then modified by natural selection.

Mutations are random. 99.999%+ of them result in non-viable organisms, or organisms that are basically indistinguishable from the parents.

Once a viable variant appears, natural selection and just luck control whether it thrives or not.

In the long-term, natural selection usually but not always leads to less damaging, more infectious germs.

In the medium-term, you get a lot of randomness.