Heat tape needs to be replaced eventually, sometimes in just a couple years. It also doesn't provide ambient heat, if your room is too cold. It works pretty much the same as a UTH. It's cheaper, but an RHP provides ambient heat and a warm side so you don't need to hassle over ambient room temps in the winter. Many people who only provide belly heat/heat tape/UTH end up needing to heat their whole room with a room heater if they get colder months, and that in itself uses up way more electricity.
You don't need heat tape and a UTH, they are the same function- providing belly heat for the hot spot. "Belly heat" in itself is not necessary, the ball pythons just need a warm side and cool side and a correct temperature gradient, whether it comes from the air or the ground.