I think you may have mis-read the chart. The rear wheel weight rating on a RAM 3500 SRW is 7,000 lbs, the weight rating on a DRW 3500 with the SAME drive line is 9,750! The GCWR difference is about 4,000 lbs. to 5,000 lbs. depending on bed length and rear end gear ratio. That would be way more than 500 lbs!
Stability is another huge factor if you factor in wind. I’m sure you’ll have opinions for both though. As for me we started out owning our first fifth wheel with a dually and haven’t looked back. With a dually you’re not that limited to what kind of trailer you can pull. Just the peace of mind is well worth it to me.
Dan