In the 2017-2018 flu season (one of the worse, which had the estimated 61k deaths in the US) infected an estimated 45 million people in the US; that's roughly in the middle of the range of the number that have caught COVID-19 so far (30-50 million the last I heard; note this is an estimate of total cases, not the confirmed 5.7 million cases, but so is the 45 million).

So our current understanding is that COVID-19 is both more deadly and more infectious.

That's fine, when we say it's estimated to be 10 times deadlier, it isn't in terms of you being 10 times more likely to die from it than the flu if you catch it, but that Covid let loose in our population will result in 10 times more deaths.

This does take into account infection rates, it's absolutely relevant and it's the big reason for Covid being deadlier, because it is more contagious.

So from the data, we see that with social distancing, lock down, and all that, it still infects and kills 5.6 times more people than the flu does every year given the measures taken for the flu, which is to have some amount of the population vaccinated. Thus assumed that without any protections, it would be even worse, possibly killing around 620k people per year. That would put it above cancer and up there with hearth disease as the number one cause of death per year.

And that's precisely why we're hoping for a vaccine. So that we can hopefully get the infections down and stop it's crazy contagion rate to manageable numbers that result on much less deaths per year, and doesn't force us to continue with the more challenging measures for limiting the spread of the virus.