No, I understand exactly what you’re saying and I agree with you in the case of arrows and musket balls. What I’m saying is, lightning does not travel the same way that arrows and musket balls do. It’s not a matter of lightning traveling too fast to dodge (arrows and musket balls travel too fast to dodge too, what you’re dodging is the marksman’s aim.) The issue is that lightning is not a projectile that travels from A to point B, it is an electrostatic discharge that happens when positively charged electrons from point A and negatively charged electrons from point B meet. If you are point B, lightning physically cannot miss you, any more than it can miss point A, because points A and B are
both origins of the lightning.
The only way a lightning attack missing makes any sense is if the lightning fails to occur at all (in which case it should do no damage on a miss/successful save) or if “lightning damage” is not actually lightning but a projectile of some kind of magical energy that electrocutes the attacker on contact. And in the latter case, yes, you’d be dodging the caster’s aim rather than the projectile.