Alright, I came off as a bit of an ***...can you confirm whether or not this tech is safe to use on the Pro or Gamecube controller? And why is this tech unsafe, but regular play isn't? (or is it?)
In my opinion the tech should be fine on a Gamecube controller. As long as you are able to grip the controller tightly (not death-grip tight) with your right hand, you should be able to prevent your thumb from going too far out from your wrist during the motion and causing problems.
I don't own a Wii U Pro controller, but as long as you can get the same kind of tight grip with your pinky and ring finger as you move the control stick back and forth, it should be fine. I cannot say for sure, of course. I am not a doctor. If you have any doubts about any of this, trust your gut.
I feel Perfect pivoting is unsafe on the Wii U Gamepad because it's consistently pretty intense on the thumbs compared to normal play. Even the most impassioned smash attacks don't require that you flick your thumb all the way across the diameter of the control stick. There's more that can go wrong in the motion and the gamepad simply doesn't provide the same level of support for the hands that other controllers do.
Normal play on the gamepad is NOT unsafe, but high APM will screw up anyone's hands on any controller if they don't take care of themselves.
If the reader is worried about it, Look up some hand stretches (such as the ones in the Staying Healthy thread I linked to earlier), and make sure you do them before you play for long periods. Remember to take regular breaks as well, and stretch again after the session is over. You'll be fine.