So usually you’d shoot the dog as it’s coming to attack you. A benefit of a gun is that it’s a ranged weapon.

How would pepper spray be more useful than a gun? As someone that’s been charged by an animal on a hike, the noise (which doesn’t require effective aim like pepper spray) is enough by itself.

Wild dogs don’t simply show up out of nowhere and start attacking

They do, actually, that’s how pack animals hunt from the perspective of prey.