.... can you see any plausible evidence for this?
The annual flu death pattern has shown a pretty steady decrease over the last 50 years, helped enormously recently by the wide availability of vaccines, so it would anyway be expected that we would see fewer people dying of flu. It's old data, but the pattern from 1968 to 2008 shows this trend very clearly.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2870877/Se figure 1. There are good years and bad years, but note how the severity of the bad years has been steadily decreasing over the period.
It's not that the mutations have been less virulent, more that our responses to them have been more effective.
Constructing an argument that says 'more people would have died if flu was worse so they are dying of C19 instead' is pretty faulty logic in my view as it's not taking into account the efficacy of the response.
