I don’t make these very often; if I want a cocktail rather than neat bourbon, I usually make an Old Fashioned.
Saying that, I find personally that when making these less is very much more and only use a ½ measure of the vermouth and a drop of the bitters.
Old school cocktails like martinis and manhattans are booze heavy and frequently are not to the taste of your average dinner guest (that’s not to say that any of your dinner guests are average).