Batman wins vs Joker 7-3.
Anyone saying diferent has no idea what a good keepaway Batman looks like. End of story.
I think you're being generous with that.
The reason people disagree is because it's almost even vs a rushdown Batman, which is how most play. A zoning Batman however... Oh god...
MMH definitely 6 4 based on the tools both have. Since MMH is great at zoning and counter zoning, he make it hard for joker to zone and for joker to get in. Also MMH's offensive/oki game is nasty and that will make it quite hard on joker. Also MMH's will do him well if joker tries to come in/ is good for MMH to keep joker in the corner. MMH's wakeups have to be respected, so that will stop up joker's offense unless he wants to get pushed back.
I had a chance to play this MU quite a bit Saturday, and while all that you say is true, Joker has ways around a lot of this stuff. For example, if I place close teeth on the ground, teleport no longer works (I can convert off of teeth even if you hit me with the teleport) and I recover fast enough to block your projectiles if you reacted to teeth (If you read teeth though I will get hit.). We can also hit you out of projectile startups on reaction (Except the MB spire). That said, you have ways to punish everything we do at full screen with a proper read and with the exception of teleporting into teeth, we don't punish you too hard for a bad read.
Due to the previous stuff I said, everything just becomes mindgames, similar to when playing against Raven actually. To stop me from getting in, you have to predict what I will do since I can punish you for guessing wrong or throwing stuff randomly. Similarly, I have to make sure that you can't read me, because otherwise I get blown up.
In close range, both characters have nasty oki games and trap set ups. However, while we also both have high/low mixups, MMH definitely gets more off of them than Joker does (Our highs tend to suck for the most part unless we already have teeth on the ground...). That said, Joker can make pretty much everything safe on block thanks to acid flower or can use blockstun to set up teeth traps. From my experience, it felt like MMH had to commit to his 50/50s since he doesn't seem able to hitconfirm his strings and was punishable if he guessed wrong. Is that the case or was my opponent messing up?
We also both have good wakeups, and both of us have ways around those wakeups. Your wakeup is a pain in the ass, but if I don't see MMH tech roll when I end a combo with teeth on him, I'm assuming the wakeup is coming and doing MB F3 for an armored near-unblockable. Joker's flower can sometimes get him out of your oki traps too, but if you modify your timing/spacing to accomodate for it then it isn't too much of a problem. I actually didn't think of trying to tech roll though.
All that said, I do agree with the 6-4 ratio because while it all feels pretty even, that changes the moment you hit your trait. Your trait makes you decimate us in mid range for as long as it's active, and mid range is usually a pretty good place for Joker to be.