why does it have to be one or the other? I think yonkyo is both...
The nerve pinching isn't an end to itself as many of you have agreed, since there will be those minority who would not be affected by the pressure point. But for most of us, it helps to put our mind there in our hands and therefore losing our center thus making it easier for nage to take our balance.
The leverage in yonkyo, as in all our techniques must also exist. you can't force someone with just the nerve point to move where you want them to move. The worst it'll do is for them to rip their hands out, and then where will you be?
Besides, getting the nerve is not through pressing it with force, but more to do with extension of the arms outwards. This I presume happens naturally when you go for the leverage.