It depends how you look at it. Omicron had a lower CFR, but higher transmissibility, so arguably worse.
There is no inherent selection pressure on viruses to mutate towards being less aggressive. Omicron had a transmission advantage that coincided with being a bit less lethal, but often being more transmissible correlates with being more lethal (e.g. delta variant).
We could have easily had a more lethal omicron variant emerge if it wasn't for vaccination effectively halting the pandemic.
Far more people were saved by vaccination than any luck on random mutation in the virus.
> With time, treatments improved
They did. Like the use of dextramethasone. Still a small improvement compared to the dramatic success of the vaccines.
> and so did the outcomes, regardless of vaccination status.
No. Vaccinated individuals were better off in pretty much every measurable statistic. By any reasonable measurement vaccination saved millions of lives.