A core legal factor in lethal self-defense is "disparity of force": if the attacker is significantly stronger/abler than you, and will use that disparity to cause grave harm, you can use deadly force precisely because it is your only viable equalizer. As such, a non-lethally-armed attacking healthy male can be shot by an invalid or a woman (among other disparity scenarios). I (healthy male) cannot legally shoot an unarmed attacking healthy male ... but my wife or father-in-law can.
The thing about a less-than-lethal attack is that the attacker is attempting to create a disparity of force. I could take on a common thug mano-a-mano, but if he comes at me with pepper spray or such it is clear he is conciously trying to weaken me to create a potentially lethal disparity of force. I can block strikes & do takedowns under normal conditions, but if I can't breathe or see due to a blast of Mace, he'll have no trouble breaking arms or smashing my head. If there's any reason to believe he's trying to create a disparity of force, I'd better use my equal or greater ability before renedered helpless.
Attacks with less-than-lethal weapons are an attempt to gain a lethal advantage.
Just as it's ok to shoot an attacker attempting to disarm you of a pistol because if you don't he'll have a lethal advantage, it's ok to shoot an attacker using less-than-lethal weapons precisely because if you don't he'll have a lethal advantage. Just be sure that the lethal disparity of force is a reasonable expectation.
IANAL - just my amateur opinion.