Shazzy is a skidmark on boxers of the internet but he's more than just a troll, he's enormously good at more than just Inj.
Anyway, Batman can do some basic stuff and go very far with it. I think that's what makes a character be CONSIDERED cheap. It's a enormously powerful tool or string or some such that allows a player of almost any skill level to get a ton of mileage by doing something that has little to no downside and powerful upsides.
So, Batman has J2 crossups and pretty good frame data. He's safe and can build a lot of pressure and 'time' allowing him to J2 quite a lot, it feels like an infinite to players of lower skill (so to me, it's an infinite) who can't get out of him just looping safe strings into j2's that have very very ambiguous hit boxes on top of the moves enormous rearward hitbox, which can let a super deep, super late jump over J2 still connect when kt for all the work looks like an empty jump, etc etc.
So Batman is considered cheap by some because he can just take tbe same sort 'you can't do a lot about this' gameplan and loop it vs almost any character and get huge mileage out of it, especially at lower ranks. Deadshot's pewpew. Supe's f23, etc.
Usually when I see a character defined as cheap that's why. They have some hugely powerful tool that they can use easily and repeatedly.
I don't think Batman is cheap at all personally. I also don't think he's as easy to play as people act like. He's not Ivy or somesuch, sure, but at the high end of things he has some specific and tight stuff. His 'core' is definitely not difficult though.