What gets me about vehicle manufactures and their numbers game is that very seldom does anything add up. Which scenario seems safer to you. A Toyota 4Runner pulling a trailer that weighs 4000# with a tongue weight of 500# or a Tundra pulling a trailer that weighs 10,000# with a tongue weight of 500#. Have you ever pulled a trailer that was not balanced? Can be very hard to handle.
You claim that the heavier vehicle handles the trailer the best? Let me give you another example of "towing capacity" because that's what you see that matters.
2017 Ram 3500 DRW Crew Cab Long Bed 4X4:
Three identical trucks in every way except one. Weight, size ,engine, transmission,brakes, axle capacities. Everything the same except axle gear ratio.
3.42:1 has a max trailer towing capacity of 20,520#
3.73:1 has a max trailer towing capacity of 25,020# (+5,500 more than truck above)
4.10:1 has a max trailer towing capacity of 30,320# (+9,800 more than the first truck)
9,800# all by just getting a different gear ratio. All three trucks are identical weight capacities.
Let me throw in a little kicker.....
Same truck as above but instead of crew cab it's just a regular cab. The max trailer capacity is 30,830#. That's 510# more than the heavier truck. The regular cab truck is 514# lighter than the less capable Crew Cab truck. So much for heavier being better for towing.