So there are at least two of us on this board. Nice to see.
I somewhat agree and disagree. Engineering is a science and it incorporates math, equations, theory, metallurgy, and other factors that can be calculated. What cannot be calculated is stupidity, or ones inability to operate a device the way it was designed. Misuse will lead to failure, and ultimately injury or death. Most devices have limits set forth by the manufacturer, designers or engineers. Use the device within those limits and it should not fail at least not within the warranty envelope. As an engineer I am sure you are familiar with the safety factor, and that everything is designed to have a > 1 SF (2 being the most common). This is to account for uncontrollable variables like impact loading, misuse, uneven loading, etc. Not saying we should push our equipment into these zones but they do exist for a reason. Overloading a truck by a few percent or 50 lbs will likely not make your equipment fail. Enter the weekend Home Depot dude that overloaded his 1500 by 1000+ lbs of sheetrock and made it home safely without damage to truck or equipment. However, doing it with little experience or pushing those uncontrollable variables higher will make things fail sooner even though you may be within your manufacturer specifications. Guess the point I'm trying to make is that these limits are a guide, and just because you are within them it doesn't mean things won't fail, or will fail if you exceed them by a reasonable percentage. Common sense is far more important. Everyone's definition of 'what is safe' is objective and pure opinion based. This brings me to a previous point made by a few members that triggered me slightly. A fifth wheel should never be pulled by a 1/2 ton. I don't believe that is true especially knowing the dynamics of a 5th wheel setup over a TT, and for a member to push their agenda (or opinion or fear) on to other members is just incorrect. What is more important is to know your OWN limits, and that is not something you can put on a DOT place-card. These trucks are designed to tow. Don't be afraid to use it as such just respect common sense, and know your own limits. That is far more dangerous then being 50 lbs over on GVW.
Most calculations in engineering are approximations and in many cases limited by the techniques used in the manufacture or the resolution and accuracy of sensors and testing equipment. Medicine is worse; how often is the actual concentration of a pharmaceutical even measured?
Many of the limitations of the truck are artificial Other than the Ram 2500's 4-link rear suspension, generally, the only difference between a 2500 and 3500 pickup is the spring capacity. Same engine, trans, axles, tires, brakes, chassis. But, to be Class II the 2500 has a GVWR of 10k.
There used to be HD pickups and Suburbans with a GVWR or 8600 vs 6900-to-7100 typical for a 1500 pickup. They had LT tires, 8-lug wheels, stronger axles. They no longer exist. However, for practical purposes, it is possible to modify a 1500 for maybe a 7800-to-8000 GVWR (although not legally rated since no one is certifying it) with changes to the tires, wheels, and springs.
Ford still lists 5th wheel towing for its F150 pickup. Depending on the model and options they rate it to 9100 lbs. However, they do talk about options reducing that limit. And there a few 5th wheel trailers with that low a wet weight. Maybe a gooseneck flatbed equipment hauler.
One other point, there is no calculated or experimental engineering behind the mythical 10% tongue weight for bumper pulls. Not only is the number 4.5%-to-6% in Europe and it is probably 8%-to-9% in the US after a WD hitch is adjusted. However, since trailers are designed for 10% tongue weight, unless using a custom trailer or having the flexibility to move the load, getting to 6% before WD adjustment is not possible. The only experimental papers I found are from the 1970s. Also, there aren't hard and fast rules for adjusting the WD hitch, especially with primary or supplemental air springs.