Again, trying to distinguish between those two terms seems to me pointless and unsupported by actual linguistic usage.
Yes, it’s always possible to (mis-)use a system of social conventions of some kind, whether you prefer to call it “manners” or “etiquette”, to embarrass somebody else about their social “inferiority”. But that is not what either manners or etiquette is intended to be about.
I’ll just repeat some relevant remarks I posted in a recent thread:
As the rest of your post illustrates, when people get their backs up about the existence of arbitrary social conventions like how to cut up your food, and start feeling judged and resentful about the implication that they’re doing it “wrong”, then that often leads to lengthy justifications and discussions about whether some individual arbitrary convention actually “makes sense”, and by whose standards of “valid reasoning”, along with reiterated reassurances that it’s okay if somebody wants to do it differently.
Alternatively, we can just shortcut the whole process by agreeing with Miss Manners that having systems of standard social conventions is useful, but that most of the conventions are admittedly arbitrary, and logical justifications offered on their behalf are mostly after-the-fact rationalizations. And that in any case [ETA: as Die_Capacitrix also notes], etiquette always maintains that it’s much ruder to openly criticize or correct somebody for “violating” an arbitrary etiquette convention than it is to commit the “violation” in the first place.