Even as I wrote my post, I was wondering if you would pull on that pedantic thread. You have not disappointed!
Hey, if you knew your argument was wrong, why make it?
Sure, COVID-19 is like a bad flu year. A really, really, really bad flu year, like 1918: the infamous Spanish Flu pandemic.
Actually, the example of the Spanish flu contradicts a couple of your arguments, as I'll explain below.
First, for the record, the Spanish Flu was bad because (1) it happened in the wake of a World War with drastically reduced ability to respond to any crisis, and (2) it happened before the invention of antibiotics, which greatly reduce the mortality from secondary infections. Neither of those is relevant today.
I'll bet you knew that already - but then, why bring it up?
First, partial immunity. There are lots of flu strains, but many of them are similar enough that an individual's immune system can fight effectively if they've had a different strain of flu before. COVID-19 is too novel for that.
Flu strains are similar to the extent that they are all influenza virus, yes. However, Covid-19 is a coronavirus, other strains of which cause common colds. To the extent that partial immunity is relevant, it's as relevant to the Covid-19 strain of coronavirus as it is to the currently popular strain of the influenza virus.
Also, to the extent partial immunity is relevant to the flu, it should have helped protect us against the Spanish Flu, yet you argued that was a particularly bad epidemic.
Second, means of mortality. The flu kills indirectly, by weakening the immune system and creating risks for coinfection, and it is the combination that kills. From what we've seen so far, it seems that COVID-19 can kill all by itself.
Again, influenza's facilitation of secondary infections is part of why the Spanish Flu was so deadly, so that's more an argument for flu being worse, rather than "less bad". Antibiotics have lessened that argument, but not eliminated it.
Covid-19 does appear to act more directly, rather than through facilitation of secondary infection. However, this does not mean that it's worse, just different. In particular, deaths from Covid-19 are highly concentrated in the oldest age categories, while flu can also kill young children. You could even argue that this makes the flu worse, from the standpoint of lost years of life.
Third, experience. Every doctor and hospital everywhere knows exactly how to test for flu and how to treat infections, and they have all the supplies they need on hand for both. Neither of these are in place (yet) for COVID-19.
That would suggest that the risk from Covid-19 is exaggerated, since with every passing day more is learned about it and how to deal with it. That said, testing is available, if not yet instantaneous, and we already know some forms of commonly available treatment, like oxygen and ventilators.