system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] Why isn't Ra's interested in having one of the plethora of super-powered heroes as his heir, or a skilled non-powered hero (e.g. Green Arrow)?

Batman is impressive, no doubt. But there are several super-powered figures, from Superman to John Constantine; why not choose one of them?

Hell, there are a number of heroes who ARE willing to kill and do a lot more than that, such as Green Arrow and Constantine. Why not have one of them be his heir?
gpt
Surprisingly simple answer- he doesn't really know Green Arrow or Constantine.

A large part of why its batman is that batman is the one who keeps running into his bases and demonstrating how skilled he is.  He's a fairly reclusive member of the superhuman community: most other superheroes he knows through reputation and the occasional one-off fight. Not really enough to  determine if they're worthy heirs. 

 But Batman, he has a close (if antagonistic) relationship with. He knows what he does personally, he's seen how impressive he is with his own two eyes, he knows his mind and goals enough that he might just sway him.

As with many things,  it's who you know rather then who you are. There are plenty of people who could be heirs, but Batman is the one he's actually met.