There are several books excellent at teaching grammar. My own favourite is The Elements of Style by Strunk and White (various editions exist, all do the job).
While precise grammar is appropriate for some audiences, I would discourage valuing it too highly. If the central characteristic of writing well is to put an idea in somebody else's head, then shouldn't we optimize for efficiency?
I had not considered commenting as a form of vulnerability practice, but as a person who struggles with vulnerability, it was a very salient point in your post. Well done.
I also appreciated the discussion of your heuristics, as it helped me frame the pedagogical facets of commenting and discussion in ways I had not previously considered. When I'm engaging with these sort of concepts, I struggle to frame them usefully in discussion with others. Your explanation made it easier for me to consider how I might engage in these discussions in the future.
As someone about to embark on a compulsory cross-country flight for work, I empathize with your decision process. Thanks for taking the time to write it out.
In your shoes, I would do as you've done. People who choose to travel implicitly accept risk, including the risk of exposure to people who choose not to protect themselves and those around them.