Yes and no. Yes because it's textbook, he will never ever lose. But, does ANY superhero ever lose? And by lose, actually face an enemy they cannot ever beat, they die, timeline over. All comic book characters are mary sues because they are protagonists of a story that cannot end. Compared to humans, batman is a mary sue. In the comic book "world", I do not think so. Batman is theoretically capable of achieving the feats he does, and remains within the "rules" set by the comic. Batman loses momentarily against several foes. Batman is also a flawed character by the way of values because he has an addiction to raising kids to be violent and is (detestably) responsible for the deaths of many innocent people by the hands of villains he refuses to eliminate.