If you read my thread in Yonkyo in its whole form, I was not the one mentioning pain or bruises, but how the technique works from a physiological viewpoint, as the index finger does indeed manipulate the radial nerve- this is only one element of the technique. Please allow me to quote what else I said:
"However, although Yonkyo pressure is "easier" to perform on a more slender
arm,it is possible to perform it on a thicker arm if the movement involved in exposing the radial nerve is three-dimensional; therefore the hips play a greater part in the technique than the arms.
Strong, centralised hip movement should always overcome the strength in one arm,
especially when the Uke's balance is completely taken, & everything remains in the Nage's centre."
I think that with this view as a whole,
that I also cover your point.