Stevens is a good actor, I don't really see the "Batman" though. Might make a good film Green Arrow or something.
Beyond having acting chops I just see him as sort of middle-of-the-road. He could sort of work appearance-wise, but there are people who have the look way more down than he does. He's not little, but he's not particularly big & imposing either. Doesn't really seem to have any way-out-of-left-field "totally wrong but somehow it works!" factor like Keaton either, he's closer to the role than Keaton on paper but doesn't have that weird x-factor about him either. He can do serious but he's not all that intimidating. *Shrugs* Just probably other superhero gigs he'd be more suited to.