Assuming it is generally accepted that COVID originated in bats, then it's reasonable to look at characteristics of bats that are unique. Perhaps even find a correlation between the behavior of bats and humans.
Bats are nocturnal. Most species of bats never get sunlight. One study I found as an armchair researcher points to evidence of a vitamin D deficiency in wild bat populations: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3897589/
Here is a study done back in may about Vitamin D levels and the severity of COVID: https://www.sciencedaily.com/releases/2020/05/200512134426.htm
Now consider the changes in human behavior as we have become glued to technology.
We stay inside more, we avoid the sun at all costs. This means we all likely have lowered vitamin levels (Vitamin D and Calcifediol specifically).
To top all of this off, our response has been to stay inside even more than we used to, allow tech to dominate all areas of our lives, thus worsening the problem. Also consider the populations hardest hit, there would be vitamin D absorption problems as well. Consider senior citizens who likely stay inside even more than the rest of us. This would explain some of the death rates in nursing homes when compared to the larger senior population.
Is it possible we have basically trolled ourselves with our technology addiction and the solution to this current problem is to just go outside? It can't be that simple right?
EDIT: Here is a link I just found in another thread on Hacker News showing a correlation between the two: https://www.medrxiv.org/content/10.1101/2020.06.01.20112334v1
In fact, one of the only safe ways to spend time with friends is outside. I know of many people who had socially distant gatherings outside - in the past they may have spent this time indoors in close quarters.
I don’t assume that everyone is literally staying inside any more than they were before. It’s not like the office was outside, either. Heck, the 20% of America that is now unemployed might be spending more time outside.
Reducing the risk of contracting Covid-19 is about people, place, time, and space. Sitting in a restaurant for an hour with trapped air mingling amongst talking and eating people is a lot worse than passing someone on a sidewalk. Nothing about the guidelines have anything to do with literally remaining indoors.
Also, the response isn’t about maximizing outcomes once you get the virus. It is about preventing the hospital systems from being overrun. In other words, whether or not staying home helps you survive Covid-19 once you get the virus wasn’t ever a part of this mitigation.
The government can’t make people suddenly not be obese or have heart conditions. They can’t make you eat healthy and get the vitamins you need. All they can do is stop the hospital from running out of beds and staff.
As far as your theory, I dunno. I don’t see anything beyond a very weak link. Humans are pattern builders, and we all want to shortcut ourselves to see a pattern out of very different pieces of information. I’m not going to guess either way on your theory because I don’t want to jump to conclusions.
The authorities responding with lockdown or "shelter in place" are their one-size-fits-all plan to threats. They only have a few sets of procedures, none of them tailored to a droplet-borne respiratory pandemic.
Leading with similarities to bats is unnecessary, and probably undermines your claim. There's evidence that vitamin D deficiency has a big effect on severity, and staying inside reduces sunlight-generated vitamin D, so you don't need to invoke bats. Just take vitamin D supplements get get outside.