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A lot of what you suggested is kind of silly. Contagiousness is not the same thing as virulence or pathogenicity, and you can look at things like the common cold (contagious but mild) versus ebola (harder to transmit but severe) to disprove the proposition in your second paragraph.This is actually related to the stuff I'm referring to in my cousin comment. Existence proofs are not evidence of certain behaviour. An analogous situation might be "If you see a car slow down approaching a pedestrian crossing with a Stop sign it is likely to stop". Most pedestrians will consider this statement true (as evinced by how they behave - placing themselves in range of bodily harm). However, many pedestrians know that at least one car has not behaved in this manner. Responding to someone who agrees with that statement with "Cars certainly do blow through stop signs even if they're slowing down. Here are some news articles of that happening" only marginally moves the evidence-o-meter.
Some things need empirical understanding. "Related counter-examples" do not set the likelihood of the statement to zero, but only downgrade it somewhat.
Personally, I've found my performance on COVID predictions pretty decent. My biggest failure was that I believed outdoor masking was necessary, and it currently looks like that is not the case.
We shall see if Long COVID is any sort of true long-term disease that is particularly unique or merely the identification of other symptoms that previously went untested simply because most illnesses go untested.
And of course I have no problem with anyone sounding small alarms on small studies. A sufficient number of independent such instances is how we identify common patterns. I, obviously, weight each individual such instance low but corroboration increases likelihood. Still, we'll see. Currently, my method of acquiring knowledge outperforms public CDC statements about the disease¹, so I'm at least better at this than they are.
¹ Assuming, perhaps naïvely, that they prioritize dissemination of truth over public health objectives that may temporarily be better met through carefully told untruths.