You're actually referring to a very broad range of acts. Here we're focusing on the most serious situations and the most obvious cases of violence and excessive frustration.
However, we also see that section 43 is still applied to acts that, as the Supreme Court has correctly held, are insignificant or transitory. Consequently, at this other end of the spectrum, section 43 is still applied in order to acquit persons—teachers, professors or other persons standing in the place of a parent—in cases where their acts weren't motivated by anger and they acted as they did in order to discipline the child, didn't use objects, didn't aim for the child's head and so on.
In fact, what's apparent from the case law is a fair application of section 43 to acts objectively less serious than those committed in the examples you mentioned.