It's actually been known since December that cases will rise super fast surpassing Delta levels in cases with hospitalization on a downward trend as it's displacing Delta, then it will fall just as fast as it rose.
Data in South Africa has already seen 23k cases at it's peak on Dec 17th. Down to 7300 as of yesterday Jan 7th.
Deaths in South Africa went from 11 before Omicron to 90 at it's peak. (38 before delta to 420 at peak for Delta)
Now how much of that is natural immunity vs vaccination is questionable but even in UK is showing a similar setup as SA.
Its no surprise that everyone is making this like it's the worst when it may look bad in the numbers but what about actual symptoms? How severe are those? Cases increase doesn't always reflect the intensity of it.
I think saying "known" and "will" is over-stating it quite a bit, but I get your point. Besides, end of December was only just over a week ago! Various data and findings have given good reasons to be hopeful, like the paper showing that Omicron viral replication rates are far higher in upper airways and far lower in the lungs compared to previous variants, rather than any certainty.
The unknown part was - and still is, to some extent - what will happen in older populations, or those with higher numbers of comorbidities (e.g. USA obesity levels), compared to South Africa. Only now is
London data showing how that's going, with high numbers of cases in older age groups, yet admissions declining. I suspect the outcome won't be quite as good in some parts of USA.
Basically it seems to be going fairly well
so far, although that's certainly not the same as everything being fine! Even though a higher number of admissions are incidental COVID findings, that still causes problems. Staff absences are high, but nothing like as high as in the first wave. The worry is perhaps not now about COVID itself, but that any regional surges could cripple other areas of healthcare and there'd be very little that could be done to stop that (low probability, high impact).
As for severity, yes, even though cases are massively up, (non-incidental) admissions are not up by the same amount - although they are definitely up. Numbers on mechanical ventilation haven't spiked up, and hospital stays seem to be shorter than for Delta. But don't be fooled - there is still a relationship between cases, admissions, ICU and death, it's just in different proportions - that we are only now finding out.