...I would lean forward and strike him on the base of his neck...
We eventually compromised:- I'd stop physcally abusing him if he would fly level turns to the left
You actually admit to that? Anyone whose ability to impart instruction was so poor that he had resorted to physical abuse cannot, to my mind, have been much of a QFI.
Didn't you teach him
how to select the correct attitude whilst rolling in to the turn?