The only influenza outbreak that approached 10% death rates was the infamous 1918 "Spanish Flu". In the US specifically, one of those most severe flu seasons caused 61000 fatalities and 45 million infections, or a fatality rate of approximately 0.14%. https://www.cdc.gov/flu/about/burden/index.html This is an order of magnitude lower than the 2-3% fatality rate estimate for COVID 19. Had that particular flu season had death rates of even 2%, the deaths would reach almost a million people in the US that year.

Furthermore vaccination is available and there is some herd immunity for influenza. Proven antiviral therapies exist for the flu like Tamiflu or amantadine (depending on specific flu subtype). COVID 19 only has experimental options currently, with no vaccines yet available.

Considering that COVID 19 has a far longer incubation period than influenza, it also has a greater potential for spread. Spread potential to a greater proportion of the population (due to less herd immunity and longer incubation) would mean fewer severe cases would get the proper resources to be treated, which further increases the morbidity and mortality going forward. There is potential for the health system to be overwhelmed. All these factors make it a very serious disease - far more so than the flu.