Caveat for this post: I’m not yet a parent (though I hope to be someday)
Jim’s treatment of Faye is out of line.
Nah.
If anything Jim's reaction was too rational.
As you say, you don't have children, and whereas empathy is one thing, experience is another.
Example?
My daughter had to go to the dentist.
Dentist could not pull a tooth they wanted to.
MY daughter was becoming more and more distraught as this 'professional' hauled and hauled and hauled while she was under only a local anaesthetic...
It took every fibre of my being not to haul the incompetent fecker off of her.
Even more so when they then shrugged and said... "I can't get it out. We'll just have to leave it in."
My take as a parent?
A 'professional' in charge of my child's well-being failed miserably and caused her great pain and anxiety.
(A moment which scarred her for a long time and made every dentist trip a feat of logic over sheer dread.)
So, yeah... Jim in NO WAY over-reacted and certainly was NOT out-of-line.
(In a way, I kinda blame Jeph for making the 'accident' too easy. Ripping off a fingernail with a dremel would, I imagine, cause far more pain and distress than Sam showed... Which might explain the little backlash against Jim.
Had we seen Sam in a LOT of pain and anguish (as opposed to, what, a frame and a half?) then it might be a different story.... But then, we don't really want comics full of mid-teens in agony, do we!)