Matter is energy. I was speaking to how much energy, in some form, is involved in propulsion. Rockets move more energy (as matter propellant) because they have

Matter is energy. I was speaking to how much energy, in some form, is involved in propulsion. Rockets move more energy (as matter propellant) because they have lower isp, while a photon rocket has the theoretical maximum isp. Photon rockets are maximally efficient but require that all propellant be E, not m.