The reason you see payload/GVWR/Axle ratings discussed so often is unexperienced people tend to look at only tow rating and believe that is what the truck should be able to pull. In reality tow rating is the maximum a truck can pull with a theorical trailer. TT and FW with thier associated on the heavy side tongue wieghts and large wind resistance aren't even close to that theorical trailer
Unless you are talking about a dually then payload/GVWR/Axle ratings will always be the limiting factor for a TT or FW. If you stay within those load limits you can't even get close to tow ratings with anything except a dually, other trucks simply can't carry the load that a maximum tow rating would require.