Ithaca Flues shotguns, or any of the other shotguns in the Thread about the Ithaca gun that was apparently repaired with makeshift sideplates, were not sold as Best Guns by any stretch of the imagination. Even in their higher grade iterations, they were mass produced, and mostly machine made shotguns that have served several generations well when used within their design parameters. In fact, most continue to function well even though they were used with ammo that they were not intended to use.
The hysteria and hand wringing over a very small number that have cracked frames is indeed unwarranted. I can't prove it, but I have little doubt that there have also been a small number of hand finished English doubles that have had cracked frames over the last 100 or more years. That could be due to incorrect ammunition, abuse by the owner, a design problem, or a heat of poor quality steel that was used in forging the frame. Without specific knowledge of the cause, engaging in sheer conjecture serves no purpose, except perhaps to inflate the already inflated
egos of some who wish to pose as firearms experts.
The analogy given by the OP concerning pushing passenger cars beyond their limits certainly applies to guns and other machinery. An Indy car can go over 200 mph, but the engines are routinely rebuilt after a small fraction of the miles driven by your Chevy pickup truck. That doesn't mean the pickup is bad because it won't go over 200 mph, and it doesn't mean the Indy car is bad because it doesn't last for over 200,000 miles. Nobody should avoid using or buying an Ithaca Flues or Fox Sterlingworth due to some unwarranted irrational fear that the frame may crack. That's about as brilliant as wearing an N95 mask while driving alone in your car... but we see that too.