Fwiw, I'm also in the camp that cases are an order of magnitude off and there is significantly more immunity in the population than we think. However that's a hunch and with out widespread antibody testing it would be irresponsible for anyone to act on such a hunch.
Wow, it is gratifying to see someone able to say this. Absolutely, with some luck there are a bunch of limiting factors (both that there's are harmless infections, that ) that are going to keep the epidemic from reaching the potential it seems to have "on paper". But these are unknown, these are the major unknowns and acting like we can just guestimate them and be safe is supremely irresponsible since if get it wrong, an order of magnitude more people die. A flu season? Ten flu season? A hundred flu season? Do you really want to roll those dice? To a fair extent, we already are but it's not comforting.
The world is full of factories producing a wide variety of things, including biological material. These factories can certainly gear up given time.
What makes you certain that it is possible to manufacture billions of tests?