Uh my counterexample is the Sun itself. Uses fusion on a daily basis to provide vast quantities of light and heat. What a fusion reactor does is it decouples

Uh my counterexample is the Sun itself. Uses fusion on a daily basis to provide vast quantities of light and heat. What a fusion reactor does is it decouples the plasma superhot gravity-laden center of a sun with a magnetic field strong enough to hold tiny pockets of plasma to generate energy (once we can go straight to fusion reactions using Boron) or to generate other particles which will create heat.