Doesn't the math still work with your explanation? If the same amount of spit is getting through the mask but each droplet of spit has 1000x the virus particles, you still end up with 9000% of the virus particles escaping the mask which is over 8x the virus particles with no mask of the prior variants.
For doctors and nurses, they are using PPE designed to block 95% of even aerosolized particles. Maybe 5% of any viral or bacterial load isn't enough to infect. As far as I've seen, cloth masks don't really block any aerosols, only droplets. For the few bacteria or viruses that might be more contagious than that, hazmat suits would be used.
As I understand things...
There are no particles small enough to still be considered small aerosols capable of escaping masks, that contain 1000x virions of SARS-COV-2. On the one end, the smallest particles contain 0, 1 or 2 virions. With Delta they still only contain 0, 1 or 2 virions. Laypeople have a vision of a particle dominated with viruses, due to bad drawings in media representations, when in reality, these small particles are mostly fluid and salt with only a few virions each. If 1000s of virions is what you are envisioning, you have to just stop, clear your mind and start over.
Experts went through a big re-evaluation of what makes an aerosol particle. Old, erroneous guidance was 5 microns or less. New guidance has the size going up to 100 microns. These are the particles that determine transmission. But even for these, the studies calculated what percentage per size were likely to have 0 vs 1 or 2 virions not hundreds or thousands. Larger the size, larger the probability of containing at least 1 virion. More infectious of a person, greater the probability of a smaller particle containing at least 1 virion. Virus, presumably lots of virus, however, is still expelled in particles bigger than 100 microns. There is a chemist who specializes in aerosol particle distribution (usually regarding pollution), here in Colorado who, with others wrote a FAQ about aerosol transmission about what happens to SARS-COV-2 expelled in particles between 100-300 microns.
"Thus there is a “valley of death” between 100 and 300 μm where particles typically cannot infect as aerosols or ballistic droplets (when talking at typical distances). Particles of those sizes are unlikely to participate in infection, except for coughs and sneezes where the stronger exhaled momentum propels them farther, or by deposition and the fomite route. [me: and masks interrupt this relationship by affecting the escape velocity]
There are also particles larger than 300 microns that usually are quickly dropping to the ground and aren't participating in transmission, but when someone is in close contact could be. [me: masks!]
So what we really have to know is the number of the small micron particles, capable of escaping masks, that previously contained no virus, which now contain 1 or 2 virions, and 1s that are now 2s. This is undoubtedly a larger number than before, and with no resistance via a barrier, does have an impact on transmission. That's why we're talking about a factor of twice the infectivity R(0), but we aren't talking about 1000x. The total number of these small particles hasn't increased as that is controlled by the type of breathing activity you are doing, and your physiology; not number of virions. So there is a theoretical maximum in the number of virions these small particles can deliver. Masks continue to filter out some percentage of these particles. We presumably disagree on the percentage. Neither you or I have any idea of how many of these particles have switched states, but I have seen nothing from the experts who know how the math and physics really work indicate that when you account for the number of these, and the number of virions they actually contain, it's enough to make mask usage ineffective. Large ballistic, droplets, via close contact are delivering even more virions, but since these are large droplets, masks are effective at blocking them.
But any mask is only as effective as the amount of time people actually wear it.
As for the other thing, mask usage still originated with tuberculous and 1-5 micron sized particles in the late 19th century and the mask quality available to people at that time (not 21st century medical grade). Still performed well enough to be recognized and adopted.