"probably only half less lethal" you're entire scenario is based on this nonsense. "Very mild symptoms". As of the weekend there were no hospitalisations in the UK. This is irrelevant.
Maybe it will bear out, but the oldest known omicron sample is only like a month old now. Hopefully it will turn out to be much less severe, but it just doesn’t seem like it’s been spreading for long enough in the uk (or anywhere really?) to know for sure yet