@LeeRoy1: Impossible to dodge? Yes.
Everything after this is immaterial to my point, honestly. Whether or not you can survive it
doesn't matter. I'm not talking about whether or not someone can survive a gunshot. I'm not talking about whether or not someone can hide behind cover and avoid being shot. Not really - these are factors, but they aren't the core of the argument. I'm talking about whether or not the weapon is fair at a specific level of character power, and the answer is no. The fact that, again, we have outliers of survival, or scenarios where we avoid being shot don't alter the argument at all. It doesn't change the fact that a firearm is a) more or less impossible to react to without prior notice, b) has no drawbacks and c) is capable of enormous damage at tremendous range. By addressing each of these things singly, you effectively ignore the entire reason why guns are an issue: because they represent a multi-layered problem that most mild powered characters cannot reasonably fight against. "Surviving" and "fighting against" are not the same thing.
The issue isn't solely that "guns kill people." Swords kill people. Knives kill people. Fire kills people. Nearly everything you find in mild powers can kill someone.
The issue is that guns are capable of doing so with enough efficiency, with enough damage, and at a significant enough range to tip the scales
significantly in favor of the person who's using the gun, and with no draw-backs for them. That's the reason they're a problem. Again: it's not a question of survival. It's a question of "Can someone reasonably defend against this?" It's a question of "How much of an advantage does this give me in a fight?"
The entire reason we have tiers of character power is
to avoid a situation where one character has too much of an advantage. So, by an extension of that, if a gun gives a character such a significant advantage in mild powers, the conclusion would be that it isn't fair. We allow and disallow certain supernatural powers and certain weapons based on whether or not they give an undue advantage, that's how we define the differences between one tier of power or another.
That's it. I'm just outlining
why guns are so potent weapons in the context of mild powers, and it's that potency that sees them disbarred so often. It's because they're powerful enough to make the fight one-sided, and that, again, runs contrary to the entire notion of having tiers of power.
You acknowledged every point I made in my post: impossible to dodge, easy to use, no drawbacks, and capable of enormous damage from afar. All of those things combined are simply too much of an advantage in mild powers. That's why they're disbarred. It's not a survival issue. It's a balance/fairness issue. Always has been. I'm not going to argue that people can survive gunshot wounds, because that really doesn't have much of anything to do with the point I'm making.
EDIT:: Again, we're talking purely LOW/MILD POWERED. As DLL referenced, guns are completely and totally fine at higher levels of power where a character can reasonably account for them. That's what balance comes down to -- can a character reasonably account for it? At the lower scales of power, the answer is really no. Not inasmuch as a fight is concerned.