I will let you all know a little history of seat making.with what they thought was a better way to make seats[...] Some companies like Sergeant, Rick Mayer, and others just reshape your stock seat and foam for a better fit. Some like Corbin make a new pan and build it with new foam. None of these are as good as the Russell or Bill Mayer (BMS) saddles. Tom
Everyone is entitled to their own opinion, but not to their own facts, because facts are facts. Rick Mayer seats are made similarly to the process/description you provided for Bill Mayer seats, although I'm sure the details differ. The Russell design was one way to solve a problem, but using different densities and types of foam is another way. I've watched the construction of my Rick Mayer seat, and I can assure you there are different types of foam, used strategically to obtain the intended results.
As to which is the better seat, I think it would be hard to get a bad seat (uncomfortable) from Russell or either of the Mayer brothers. Each builder has different features, that can and should help potential customers decide. I can say that after considerable research I found the Rick Mayer seat features compelling, for me, and am very happy to be able to ride all day in comfort instead of having to stop every 90 minutes. My Rick Mayer saddle and my CalSci medium windscreen have turned my FJR into a comfortable all-day riding machine.
I can't comment on the Corbin seat, but I can say that the Sargent aftermarket seat, while better than the stock seat, isn't even close in comfort to my custom seat. The Sargent is wider, but hard as a rock. Maybe they should call it the 'Sargent Rock!' At any rate, the negligible price difference between a true custom seat and the aftermarket seats makes a custom seat seem like a no-brainer.