You make a good point that a broken hand doesn't cost much in the moment if you break it with a fight-ending strike.The applicable part is that a broken/damaged hand caused by punching doesn't necessarily mean that all is lost - there are degrees of broken which may or may not disable that hand. I didn't notice I'd damaged my hand until it started swelling later in the day.
Would an adult feel more debilitating pain from the same injury?
My view on palm vs. fist is that a swinging 'slap' type open palm is definitely a more natural action for most people and takes little in the way of training to learn to aim. But once you get toward a 'direct' palm heel strike - more like a jab/cross action - then the chance of a more severe wrist injury increases greatly.
I only really included it so I could make my partly sarcastic statistical analysis...
But that said, while my assailant was still 'a kid' he was older, bigger, stronger and had a bully reputation. He was used to picking his targets based on the fact (he thought) he could easily overpower them. Is that really so different to every adult attacker? Surely not every attack (simple or sexual) starts with the assailant 'squaring up' to his/her intended victim.
A kick to the face from that position was a new surprise for him - while an adult might not cry about it the situational shock will likely work a whole lot better than an elbow that they've probably shaken off many times before.
Maybe I'm wrong about that, maybe it's possible to train in a few hours a smiley slight girl to deliver an elbow strike to a larger attacker's abdomen with sufficient force to disrupt them while said girl is off balance and under stress and their assailant is tensed in 'fight mode' - as shown in multiple videos where the instructor grabs a giggling girl from behind, leaning over her so she's fully upright then says "oof" and lets go when she gently taps him with her elbow.
A shoe in the face (delivered from a more 'real' position, where you're already leaning backwards and probably holding the attacker's arm that's around your neck) might just be enough 'shock and awe' to let the victim cry and run away instead.
Thing is, I'm far from an expert - everything I've said might be complete bs (it's only able to be substantiated by my experiences in those particular situations)...