I think where Batman really wins isn't with the common Gotham psycho, but the different kind of threats you see in his rogues. He's got secret societies with the Court of Owls and the League of Assassins, eco-terrorists with Ivy (and Ra's to, though no one seems to do that with him anymore), metahumans with Clayface, Man-Bat, etc., mobsters and gangsters with Penguin and Black Mask, eccentric thieves with Catwoman, he's even got a higher dimensional, cosmic threat in Bat-Mite. And all of them are on his A- or B-list of villains.
Flash has a lot of blue collar/one-trick foes with the Rogues, which are kind of the common, bread-n-butter of his gallery just like psycho's are Batman's. And Flash's got some major time traveling threats with the various Zooms and Abracadabra, a "broken mirror" or two like with Godspeed (and Thawne), a couple would-be tyrants like Grodd.....and getting any further than that involves digging deeper than we should have to. I mean, he's got some great foes in different subgenres or with different goals/scope, but......I mean, a cult that worships speed would definitely help broaden the rogues gallery but when was the last time Savitar got serious panel time and development? When looking at just the most well known/biggest villains, Batman's have a little more range to them than Flash's. If we got into the C-list villains, it'd even out a lot more.