When judging who's the greater fighter between two men...

No. This can be used in some situations, but clearly does not always apply- for example, if a legendary champion with over 100 pro fights and an incredible career suffers one freak loss in his prime to a journeyman who won half his total fights, does the journeyman rank historically higher? Of course not. And there's no reason this logic should stop working when the opponent moves up in class.