/s is not punctuation, it's an explanation. And explaining the joke kills it, and also insults the audience. Sometimes the ambiguity of a statement is itself powerful, as it reveals how one side can wholeheartedly believe something the other finds absurd.

One should only use /s if the comment is really so devoid of absurdity that it can be misinterpreted.

GOOD: Trump has done a lot of good for Americans /s

BAD: Trump is the greatest human ever born and is entitled to prima nocta with all brides /s

Re: sarcasm vs satire. You're mostly arguing the dictionary. The /s "sarcasm" markup is used when satirizing some POV, not just strictly for sarcasm.