There's a few other things at work here. First of all, a shotgun or assault rifle is going to be at least weapon:2, so if we're still assuming 5 shifts against an unarmored target with only a stress track of 2, they're going to be taking a 7 stress hit, needing a Moderate and Mild consequence in order to bring down to something that fits in their stress track. Most civilians are going to want a concession at this point; this gets you the same effects, but it's a VASTLY more brutal way to go about business.
Against someone actually wearing armor, or having supernatural defenses, a taser is going to have trouble getting through. Against an actual spellcaster, it might not even work in the first place.