Have a XXX mono. T Bar came loose and the stuffing tube was damaged and shaft broke. I can see why the stuffing tube got damaged, but am having a hard time figuring out how a steel shaft would get damaged that fast from a softer material. Guess I just do not understand. In any case would appreciate any comments on this.

Assuming your "steel shaft" is a common flex shaft, they are made from 2 windings of thin steel wire ( inside/outside ). When the support goes away, the prop load and engine torque tries to twist the flex in a knot. It lets go quickly.