Of the multiple actions you mention the least important is tried and true- the antibacterial effect. Yes, corona patients do often end up on anitibiotics, but there are plenty of other antibiotics to go around and that would just be a nice benefit thrown in. The over 500 patient experience is a critical reason we are where we are now- few side effects and big impact on some bacteria.
But It must work on corona in ways not tested on humans and one MOA is from an AI study and is theoretical only.
You are right to stress the critical next step- human testing. Maybe when the dust settles the immunomodulatory effect and decrease in cytokine storm deaths will be where B shines or maybe it will be direct killing of the virus or maybe none of the above.
The only truly proven B benefit in patients, though, is the least important in terms of corona success. It would be a very nice added bonus to use less antibiotics, to not add yet another drug, however.
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