Fundamental flaw:

They don't bend lightning, the simple generate and direct it as a guide, they have no control of it to any extent other than direction it initially goes.

Let the lightning go anywhere else than out of your body and you're killed by it.

Maybe because you're chi-blocked before he'd go near you.

They just make and guide it, they can't protect themselves from electricity and heat. Remember, Zuko got burned by fire, and then he caught a lightning bolt to the heart and that nearly killed him.

YFW

why didn't i think of that