(edit - for the record, this was in response to the first paragraph only, as the others were edited in afterwards)
The grains of sand example should make it clear: it is not true that this grain is one of few at the beach, but it is true that it's one of the only. This makes it a poor expression for scarcity, and while obviously we know what was actually intended (as with "could care less"), that doesn't really make it any better.
BTW thanks for the hot tip regarding the posting delay feature! Lord knows I need it, nothing induces https://en.wikipedia.org/wiki/L%27esprit_de_l%27escalier like hitting that reply button :"D
FYI for anyone reading this (not directed at you specifically): the 'delay' option in profile setting adds a delay before your comments appear publicly, giving you a buffer for edits and deletions before it goes out to the world.
Personally it helps a lot with ensuring I'm happy with the comments I make, and it helps avoid situations like this where multiple layers of retroactive changes make the conversation hard to follow.