"Omicron doesn’t confer great immunity against delta"
It is my impression that it actually does, and that is why Delta was outcompeted so fast. If it didn't, both strains would likely co-circulate together.
Outcompeting is an immediate association between the two variants. Conferring x-variant immunity means that once you've recovered from one, you will have lasting immunity to other variants.
There is a possibility that the large majority of the population has been infected with omicron, and recovered. But then delta could come in at that point and produce another wave. At this time, the body would be much more successful at holding off omicron, but maybe not so much with delta.
So purely from the fractions of current infections, you cannot draw conclusions about x-variant immunity.
It is my impression that it actually does, and that is why Delta was outcompeted so fast. If it didn't, both strains would likely co-circulate together.