Boy, it's been quite a while! Have a half-assed conclusion (/retrospective/answer).

Here's an article with a lot of illustrations whose models suggest that increased ventilation (in several common scenarios) results in a reduction in infection rate by a factor of about 5-7x, even when compared to mask wearing.

A room, a bar and a classroom

https://www.microcovid.org/ 's model seems to be using a 5x reduction number for indoor vs "almost-outdoor," which seems to roughly line up with this.

For comparison, mCov's factor-reductions for surgical-mask wearing are 2x, and n95s are 10x. So "open-windows and heavy ventilation" lands basically right between the two in reducing risk.

My impression at this point is that adequate ventilation was a pretty strong target for reducing spread.

So... Kudos or BayesPoints to ChristianKI (whichever you prefer) for calling that 8 months ago.

Here's a good op-ed on this topic: https://www.nytimes.com/2020/03/04/opinion/coronavirus-buildings.html

The author suggests that the lack of attention on building ventilation is due to uncertainty about how important close contact (i.e., close enough that a person's respiratory droplets could directly land on you) is for transmission, vs. more indirect airborne transmission.

(E.g., from CDC website: "Early reports suggest person-to-person transmission most commonly happens during close exposure to a person infected with COVID-19, primarily via respiratory droplets produced when the infected person coughs or sneezes. Droplets can land in the mouths, noses, or eyes of people who are nearby or possibly be inhaled into the lungs of those within close proximity. The contribution of small respirable particles, sometimes called aerosols or droplet nuclei, to close proximity transmission is currently uncertain. However, airborne transmission from person-to-person over long distances is unlikely.")