You talk about disparity of force, and that self defense must be proportional to the threat. You’re right to focus on that. Because that’s what the DA will be focusing on.
You might be legally able use a hard punch to stop an attacker who is stronger than you. But try that against an unarmed little girl (as evil as she may be), and the DA will throw the book at you.
Is that fair? It doesn’t matter. Because all that matters is whether or not the DA thinks you used excessive force.
Excessive force has to be determined by the level of threat. A pack of out of control little girls is not a minor threat.