I will always insist to my grave that Superman slightly beats Batman 5.5-4.5 or something if he adheres to the rules of fuzzy-guarding Batman's mixups and pushblocking at appropriate times. He outdamages Batman in just about every aspect of the match and can harass Batman on wakeup just fine. His D2 is decent to use against Batman's J2 even if its no Aquaman D2 and he can bait Batman into teching all kinds of throws with the use of MB3s.
I view it this way. When Aquaman has a life disadvantage on Batman, he cannot resort to spamfucking with FTDs anymore since the chip damage and trade game will be in Batman's favor. Superman, for the most part, can always resort to the laser game to chip Batman down or keep him out no matter how bad his life defecit is (assuming Superman isn't in True Master territory). Does Batman wants to Bat Grapple in between laser loops? Fine, try Bat Grappling between ground lasers on block hoping that I don't meterburn them. Want to jump my lasers on reaction? Fine, give me all that meter to push block you and hope you don't get spanked with a 12-15% straight laser or 17-19% heat vision if I make a read on your jump arcs.
There's more that I can't really think of since I haven't played the matchup in a while. I always felt when I lose to Batman players, I got badly outplayed. However, that number is extremely controversial to some so you don't have to put it if you don't want to. I'm fine with 5-5 I guess.