> If it was actually covid-19 community spreading in December, then we wouldn't be talking about a few thousand deaths now in April, we'd be talking about millions.

That's assuming the death rate is as high as it is estimated from known cases. If the actual death rate is a magnitude smaller due to huge amounts of undocumented cases, then the curve is wrong.

Going by some of the antibody tests performed, this seems to be the case, but the antibody tests might be erroneous as well.

There's a strict lower bound of around 0.5% on how mild the IFR can be looking at NYC and Italy

https://www.medrxiv.org/content/10.1101/2020.04.18.20070912v...

There's absolutely no way that it's been running rampant since december

Hell no. That estimate comes with many assumptions, so unless you are willing to list them all, it is better to just provide the link. And it is still just one study, waiting to be proven / disproven. Take it easy and use common sense.