Crash I know that you are reading the section on electricity damage correctly. However the -2 is very much like the disorientation toxin effect.
So if you shoot a dragon or someone in full body nonconductive armor, or anyone else who takes no damage, this might not be considered a "successful" attack. Just as shooting a cyberzombie with a light pistol would not be a successful attack.
I disagree mainly on the point of what you are considering t be like a toxin. The electric damage causes a "resistance" of Body+Willpower(3) (+half impact armor) or you become incapacitated. To me, this is the toxin like effect. The -2 is what occurs if you successfully defend against the toxin affect.
Before we go any further, do you have to damage an opponent to cause them to resist a toxin? Dart Rifles, Splash Grenades and the like do no damage on their own, they just have to "successfully" hit the target to make use of their payload. So with a normal toxin attack it breaks down like this (using a Dart Rifle as an example):
1. Attacker rolls to hit target and gets 4 successes.
2. Defender rolls to defend and gets one success. The Dart Rifle require 2 net successes to deliver its payload and the attacker got three, the attack is successful.
3. Defender resists the Dart Rifles damage (which is zero).
4. Defender must resist the loaded toxin (using Gamma-Scopolamine as example). Defender rolls body for four successes, but the drug has a power of 8. Defender suffers ill affects of drug.
Now if the the defender had gotten eight successes, the drug would be completely negated. Either way, the resistance is in no way tied to the delivery attack of the toxin.
