Yeah that's fair -- there might be some high-exposure situations (like being coughed on) where infection is very likely with or without a face shield.
I suspect that a lot of airbone infections are from inhaling small doses here and there though, considering how long mucus droplets can stay suspended [1] --
> Particles of diameters 1-3 μm remained suspended almost indefinitely, 10 μm took 17 min, 20 μm took 4 min, and 100 μm took 10 s to fall to the floor.
[1] https://www.mintie.com/assets/img/education/Aerosol%20transm...
With an exponential curve, whether you start off with 10,000 or 100,000, given that it takes about 2 weeks for our adaptive immunity to kick in, the virus is going to be in the hundreds of millions in either case.
[I work in vaccines, but not as a scientist, so I'm just trying to absorb as much as possible here..]