I pulled empty car and equipment trailers with mine, no ill effects. Pulled just over a ton of scrap once on a ~700# trailer too, I'm sure that had some healthy tongue weight. The rear coils broke as the next owner found, but when he removed the hitch it unbolted and all was straight and true as intended. it's got the wagon rear coils in it now, that I'd intended to install but never did...
I think you were seeing results of overloading a terribly poor hitch design (perhaps the usual US-spec hitch that through bolts the spare tire well rather than somewhere with some actual meat to it?)