What I think you are having a problem with are the thickness standards for letter mail. They are of somewhat recent vintage ~ I wrote the first ones.
What you need to do is quit stuffing all that extra stuff in the envelopes, particularly if it's advertising. Send that at Standard Rate rather than at a marked up First Class Mail rate.
I think you need to move over to DU and not go telling FReepers what they "need" to do. As it happens I frequently mail disks in a 5x8 envelope with a piece of paperboard in there as a stiffener. The cost of this tripled with one of the recent penny increases. I really do not care whether my stuff doesn't go through the automated machinery. Maybe we could just through away all the automated machinery, cut the forced two minute conversations about whether I want to send my non-standard envelope by registered mail, whether I want delivery confirmation, whether I want to purchase any stamps, etc., and fire half of the postal workers starting with the ones who cannot speak English. (Or at my Post Office, the Box Mail attendant who is deaf and cannot hear the buzzer mounted next to the box mail window.)
ML/NJ
Time to consider the practices of John H. Reagan, the Confederate Postmaster General. Reagan promoted efficiency in the office and reduced costs. He ran the only post office in history to turn a profit.