Well, here is my take on this argument.

There is a condition for constant motor RPM to achieve the constant ground speed: the plane is in a level flight with almost constant wind heading and speed. While the latter is ideal, we sometime can encounter during a season, dependent on where we locate. Let us not forget this context.

More importantly, that the voltage of a main battery pack will drop during the course of a sequence is a unique problem to EP. For a range of throttle positions, the gradual reducing RPMs due to dropped voltage is an extra variable to manage. If ESC can take this management job away from the pilot, it is something.