The thing about the Short Circuit is that it completely breaks counter play around the Engie
A Demoman goes from THE sentry killer to a useless fool whose weapons are all either melee or don't work because of the Short Circuit
Soldier, who's probably second choice for destroying an SG, is similarly countered. Trying to destroy a sentry with a shotgun isn't gonna get you anywhere, Uber or no.
So now who busts sentries? Spies and sometimes Heavies. That's it. A good SC Engie can completely negate the two main counters to his sentry. It's not about tasing the player to death, it's about stupid good sentry defense.