The answer is simple and has been proposed prior. Go weigh both trucks and then subtract the weight from the GVWR of both. Make sure both are loaded about the same for comparison. Then, forget the discussion as it has no merit, is an argument with a Ram hater, nor are you going to gain anything winning or losing. It just does not matter. Many haul truck campers or tow fifth wheels with trucks that are a little over gross. It just does not seem to matter in the real world.
None of the door sticker or documentation includes dealer installed accessories like bed liners, adding or changing wheels and tires, etc. So, who cares really what the sticker says? The only thing really important is what it weighs at the scales dedected from the gross weight. No sticker or documentation means much if the truck is modified at the dealers.
We had a huge discussion (debate) last year on this forum about what is included in gross weights, payloads, sprung and unsprung weights. We went into the CFR's (Code of Federal Regulations) and looked up the definitions of Gross weights, Axle weights etc. At issue was whether the axle and tires are really part of the gross weight since they carry the truck's weight so should they be part of the payload calculations. It gets complicated as some change out the tires, wheels and axles to heavier to carry more load while technically if it adds weight it reduces payload. While it does not change the manufacturer's gross weight calculations, it does often allow for more load carrying capacity even though the original manufacturers's documentation would say otherwise. Perception sometimes in not reality!
These debates with your Ram hater friend are similar to the almost useless debate about a one ton is a three quarter ton with another spring in the back. Look at Ford's towing guide and in some cases the gross and payload numbers comparing a SRW 350 and a 250 are almost identical. So where is the real difference as there appears to be little until the one ton adds two more skins in back, a heavier axle and then the gross and payload differences are huge. So changing the axle to heavier and adding more springs and tires does change what a SRW350 can carry if the manufacturer does it; but not if the owner does it (at least as documentation goes).