Yeah, that’s pretty pendatic. Text emoji is kaomoji, which is the Eastern branch of emoticons, so technically it wouldn’t generally include o7, but that’s kinda splitting hairs.

You’re also right, o7 has more broad uses than F, but they do both get used in a usually tongue-in-cheek “condolences” manner. So you can almost always use o7 in the place of F, but not necessarily the other way around.