I was unaware of the heat-treating issue surrounding BP guns..but I will truthfully fall into that demographic (probably) of playing with BP as an avocation and an aside to my cartridge toys.
I've been shooting BP guns seriously for about 2 years now since joining the N-SSA. I've had heat treating problems with virtually all of the BP guns I have.
I've had springs go soft in locks, you can see hands get worn on revolvers, and everyone knows about the soft screw heads that damage so easily.
I used to wonder that a BP revolver can be sold for $200 but a cartridge revolver, which is nearly identical in terms of machining operations, costs twice or even three times as much.
I'm pretty convinced that the reason why they are so much cheaper is the heat treatment and metallurgy. They know that a cartridge gun will be fired thousands of times in its life. It is trivial to shoot 5 rounds at a session with a cartridge gun. It has to hold up not only to repeated and often use but the high pressures of modern smokeless loads.
But a BP gun might not get shot by many buyers 50 times a year
. A fair number of BP shooters no doubt shoot them once, discover what a comparative dirty mess they are, and put them on a mantle or in a closet. It's only when you use them a lot, like shooting them 50 or more times a month, that you discover their shortcomings.
While I've seen actual broken parts, usually the problem is related to poor heat treating.