Hi Rodney
I have never had a muffler thru rod break. Every one of my mufflers has one. I make certain that nothing is ever loose on them. According to your theory, the head bolts should also break. Or the muffler to engine bolts. I have seen other people break the muffler thru bolts. They seem to be the same people who do nothing about the muffler being loose unless it falls off, once, twice, three times. The "if it does not break, why fix it" philosophy. To each his own.