One universal antiviral to rule them all?

Wont viruses just adapt and now we've got worse viruses as a result? Isn't this kind of why doctors don't like to prescribe antibiotics too often, because they become ineffective in the long run.

I'm genuinely asking, I'm a simple software dev not a doctor.

1) Viruses don't adapt instantly nor perfectly - that's why viruses can be animal-specific. Influenza (or recently SARS-CoV) are famous because they are malleable enough to adapt to new hosts, human or animal, within a few months or years, but not all viruses have this ability.

2) To further illustrate, some viruses have been nearly eliminated with a single vaccine. Polio didn't manage to adapt before going almost extinct. And a good reason why is:

3) Viruses can only evolve inside contaminated hosts. If you find a cure that stops quickly the virus from multiplying and contaminating, you are also curtailing its ability to adapt. A contaminated host is a giant casino machine, allowing the virus to mutate until it hits a new evolutionary step. A strong enough vaccine or treatment is like throwing out the virus before it has time to play much.