you were saying that you wanted to get rid of the spot light sooner or later. thats ok but you will still need to provide proper ambient temps. a UTH providing belly heat is good but will not raise ambient temperatures to where they have to be.
no type of temperature is more important then the other but if i were to say which one you could live without then it would have to be belly heat over ambient.
if you had an ambient temperature of 90-94 on the hot side and 80-82 on the cool side the snake would live a healthy life where as using only a UTH would only create lets say a 92 degree hot spot with air temperature being determined by whatever the room temperature is.
that can be compared to holding the snake in the palm of your hand in open air. your body temp is 96 point something degrees so holding the bp in the palm of you hand in open air is just like him sitting on a 96 degree UTH on the warm side of the tank.
so a UTH hot spot with room ambient temperature will not be enough to properly support you ball python's thermoregulating needs.
unless the UTH was thermostatically controlled at 90-94 and the room temperature at 82.