Probably not. But, while an air-breather would be more useful on a larger planet, it would still be the case that almost all of the space launch system's work m

Probably not. But, while an air-breather would be more useful on a larger planet, it would still be the case that almost all of the space launch system's work must be done outside the sensible atmosphere. Air breathing would only add the tiniest margin to "chemically escapable planets."