Wally was taken down by a tree root while he was super speeding, and would no doubt probably run through the bale-fire to try and rescue anyone caught in it likely without realising that doing so is inevitable suicide.
Kyle's ring has limits and I have no doubt the nature of the balefire would be attacking the willpower required to sustain it. All it takes is a single little crack and he's toast.
J'onn would be up there watching his pals get slaughtered. And he'd inevitably have to come down out of a sense of obligation as they fall or else he stays safe, doesn't fight the dragon and therefore is not affected by the prophecy. Of course, given the the dragon has mind affecting magick and J'onn inevitably attempts to psychically probe opponents, I imagine he'd be quite badly fucked up.
Superman dodge? Please. He's a brick who relies on his invulnerability far too much. By the time he realised that it wasn't just ordinary flames washing over him, he'd be a candle on the wind.
Similarly, Batman ain't going to be dodging no area of effect attack, relying on his flame proof undies and friends like Superman or the Flash to try and carrying him out of the flames. Or he comes at the dragon via Batwing and is simply swatted out of the sky then eaten off his parachute when he ejects.
It's not the call the others get to make because they're ignorant disrespectful mortals too full of pride to treat the situation with cold rational logic. PArt of being friends is watching out for them and stopping them when they're going to do something stupid like enter into a battle that will 100% kill them all when they don't have to. See, Diana absolutely trusts Superman to have her back, and she absolutely knows he'll die if she lets him.