There is no reliable way to calculate the Case Fatality Rate (CFR) for flu, because it is not a reportable disease. That is why the CDC can only estimate the number of illnesses and the number of deaths. To calculate a true CFR you must have confirmed/tested illnesses and then know the outcome of those illness (recovered or died).
Therefore, anyone who says something like “Covid-19 is 10x more lethal than the flu” cannot back up their statement with data. Dr. Fauci has said that, but I would really like to “see his work.”
It is just statistics. If you have 100,000 flu diagnoses, and 100 of them die from flu-related complications, you can say with high confidence that the CFR for the flu is 0.1% across the population at large.