RDEs are more efficient than regular rocket engines. Also, a big part of engineering rocket combustion chambers is balancing power with combustion instability,

RDEs are more efficient than regular rocket engines. Also, a big part of engineering rocket combustion chambers is balancing power with combustion instability, which can cause flame-out at best, and rapid unscheduled disassembly at worse. RDEs lean into that high energy stochiometric reaction to eke out more efficiency. Due to the tyranny of the rocket equation, even a modest increase in efficiency can greatly increase payload to orbit.