> Recent seralogical studies indicate that the number of positive test results are likely a small fraction of the total number of cases

No: the antibody tests were done with the expectation that the total number of the infected would be much higher. The tests have such false positive rates that with the results actually observed the tests in most of the cases say nothing -- in most of the locations the numbers would be similar even if nobody would be a real positive. And there where the results are above these "noise" thresholds we also have a big numbers of deaths which do confirm my claim of order of magnitude deadlier than flu.

Even observing the pure death statistics we can see that, even in spite of all the measures actively taken throughout the world. Without them it's obvious it would have been again the difference of some orders of magnitude:

https://www.euromomo.eu/graphs-and-maps/

See also here:

https://www.ft.com/coronavirus-latest

the "Death rates have climbed far above historical averages" graph.