Wow! You have conviently ignored one of the strongest contenders in the Ram. The bigger V8 in the 1500 has some really strong towing numbers.
One other mistake in your post is your looking at hypothetical numbers put out by the mfgs. Real workd payload is the result of the vehicle loaded ready to travel subtracted from the GVWR as listed on the drivers door post. Since Fords are historically heavier to begin with they usually list higher GVWR numbers so at the end of the day they all have nearly identical cargo capacity.
While a 1500 series might be OK today, what if you decide to upgrade next year? Are you going to have to upgrade trucks too? Gets really expensive to upgrade both. Why not get a 2500 today and if or when you want a larger heavier trailer your ready with a suitable truck.