You are fundamentally correct that moving the axle rearward so the camper has less overhang is good for weight distribution and towing.
However, in the real world, a diesel F450 is gonna handle any camper just fine and still have plenty of weight on the front end. Remember, it starts with a whole lot of front end weight already!
As for trailer towing, I sometimes have a 10,000 trailer behind my camper and I achieve the proper physics by stretching my trailer tongue to reach the truck rather than making matters worse by using a hitch extension which does the opposite of what you want to the weight distribution and handling.
If you really want the rearward axle placement, a cab & chassis of the wheelbase you prefer and a flatbed is about the only practical way to get it. But I don’t think you really need it with one of these new trucks.