Most recent common ancestor of Alpha, Delta, Omicron-1, and Omicron-2 now estimated to be around July, 2017.
Influenza-like illness increased in winter of 2017, before the Wuhan-strain escaped China.
As for why the flu disappeared during the 2020 flu season, possibly because CDC counted those cases as COVID due to an inability by PCR tests to differentiate between the two viruses.