It's kind of amusing to contemplate a situation with two people, one armed with a gun and one with a knife. The knife bearer threatens the other and approaches him with knife out and showing obvious intent, but you think the other person with a gun cannot fire because his weapon is superior? So, he gets gutted and killed?
Armed is armed, the ability of the weapon to project force at a distance is irrelevant.
Justification is based on this, armed or not and clear intent or not. It's silly to pretend otherwise.