A vehicle's tow rating has a lot more to do with its design and construction than its weight. Consider a diesel tractor in a tractor-trailer combo where the weight of the trailer and cargo is often some multiple of the weight of the tug; at the other end of the spectra some cars are rated for zero-tow-weight. There is no golden ratio.
Off the top of my head, some of the things that affect tow rating are
-- The TV's brakes
. They have to be able to effectively handle the TV & Trailer.
-- Wheel base & weight distribution. A longer wheelbase and shorter distance between the rear axle
and the hitch helps maintain front-tire traction; vehicles with shorter wheelbases and greater hitch overhang loose traction and directional control as the vehicle's effective center of gravity shifts backward when weight is applied to the hitch. (Additional downward weight beyond the standard hitch weight is applied to the hitch while braking and as the TV and trailer go over rough terrain.)
-- Rear axle
. They also have to handle the added weight and demands of towing.
-- Body/frame type. Cars and trucks with traditional frames have stronger mounting points for the hitch than frame-less "unit body" vehicles.
And the list goes on and on . . .