Since they both can beat the JLA who could win in a random encounter
Prometheus managed to beat JLA only with immense amount of prep, and even so he was not able to defeat superman, so he tried to make him commit suicide because he couldn't kill him by himself.
With unlimited prep there is a 5% chance of him wining, without prep:
"The General. Beyond curbstomp."
It's true. Neural chaff is perfect for taking down the General. Batman almost beat him by hypnotizing the guy.
And not being able to think on his feet is true too. He's been taken down hard by Batman and Green Arrow alone when he isn't ready for them.
Moreso than even the Bat, Prometheus is all about prep time.