That statement makes zero sense. The transmission back doesn't see an "oscillation" - it doesn't matter if you have a piston or rotary motor. Even if you have a piston engine, the motor still only consistantly spins one way (the crankshaft doesn't go back and forth). Obviously, no motor oscillates it's output to the transmission.

The reason that the tranny, rear end, driveshaft, etc won't hold up is simply that they were not designed to be strong enough to hold the higher torque outputs.

The diff on the N/A driveline is pretty weak, but again it comes down to torque outputs. It holds up fine to daily driving, just won't handle drag starts. Whether the motor is piston or rotary doesn't matter. And it doesn't matter if it is a 500hp motor or a 200hp motor. What matters is how much torque is being placed upon it.