Again -- it's just not that easy.
"Big scary guy" vs. BJ Penn? BJ would probably have a hard time justifying resorting to lethal force.
"Big scary guy" vs. me? Depends. Am I sick, injured, already exhausted by a foot pursuit?
"Big scary guy" vs. this guy
? Probably.
The justification for the use of lethal force is that you reasonably were in fear of imminent grievous bodily harm or death. Part of the determination of the reasonableness will consider any size/age/physical disparities between the two people.
I'm not familiar enough with the case
geezer described to categorically state it was or was not reasonable. I will note that, unless you're on the high seas facing pirates or something similar, a "warning shot" is not a good idea, and a waste of a bullet that you could put where it'll do some good.