I mean I get the complaints about their being a supposed lack of Batman turning bad compared to other heroes
Although there are more than a few examples of evil Batman(especially now with the dark multiverse) none of them are really satisfactory
To name a few
Batman who laughs
Owlman
Thomas Wayne Batman
Wrath
I'd like to also include Injustice Batman here but he's not really considered evil just a non ideal Batman in a messed up universe
Anyway what makes a good evil Batman
I mean realistically out of all the ones listed I think an amalgamation of Thomas Wayne and BWL would work
He needs to be a threat not just to Bruce but the entire DCU but he also needs to not be a meme like how BWL has sort of become
Ideally you should highlight all of Bruce's negative qualities and play them straight. Bruce is at his worst insane, abusive, paranoid, single minded, obsessive, etc just all the bad stuff you typically see with an off the rail Bruce
Consequently none of these traits are featured in any of the above Batmen. That's a problem
Its like in an unintentional way you are still writing these characters without flaws and that needs to change