Will something snap? no highly unlikely anything will snap, not unless something has been incorrectly fitted or is loose.
The towbar itself is basically massively over engineered so any loads on that are transmitted into the chassis
The chassis members to which the towbar is attached is indeed relatively very much thinner, however, it's pressed into a box section which gives it all the rigidity it needs, because that is, as an integral part of the whole chassis, it readily dissipates the loads imposed by the attached towbar away into the surrounding metalwork.
So the metalwork is not the problem but the affect the noseweight has on the car as a whole while on the move.
Think of a 75kg, (12 stone), sledge hammer?!, as a static noseweight this nothing to the affect that weight has as a 'hammer blow' pushing and pulling on the towball, this as said is easily absorbed by the metalwork but finally has to be dissipated by the cars suspension, and this is where the real problem lies.
If the noseweight is so high that the rear suspension 'bottoms out' while on the move, then the energy left is going to try quite successfully to lift the front of the car with instant loss of control of steering.
Lesser amounts of excess noseweight will have reduced affects but at some point could be enough in what might have been just a bad situation?.... to turn it into catastrophic!!