I think I would want to see a metallurgical study of that fracture before I assumed that it was a shear and not tensile break. I don't want to be the one that finds out when one lets go.
The poly bushings are much more resistant to vertical motion than either the rubber or spherical, but I have used them (Prothane) in the past on my '71 Mustang and have been able to pull the strut into position on the lower arm with one hand so they aren't that bad. I have a hard time seeing that the bushing could exert enough bending force to shear a strut rod even though there is more side loading than with the alternatives. Has anyone had one just bend without breaking?
I don't know of any aftermarket strut rods that are advertised as being tougher than the OEM and are direct replacements. Opentracker has a unit that looks fairly stout that might ease my mind, for one...
http://www.opentrackerracingproducts.com/strutrod/