That statement seems like complete nonsense to me before you even think about roles - a Martini only has two ingredients - gin and vermouth (and an olive/pickle

That statement seems like complete nonsense to me before you even think about roles - a Martini only has two ingredients - gin and vermouth (and an olive/pickled onion/oyster/mothball/whatever as a garnish). It makes no sense to say "replace all the ingredients, and you get this other thing" - no shit.