He is subservient to Yaacov, but only up to a point. Esav has the power to remove the yoke, and take his turn at leading. This can help us understand the meaning of the gemara, and the words of the Maharshah. Not only is the Maharshah talking on the political level, but also inside each man. The moon's complaint about two rulers sharing the same crown, is an observation about human nature.
Man is incapable of having two primary goals.
Each person most choose between tum'ah and becoming a slave to his body, or taharah and purposeful existence. G-d diminishes the moon. This seems like a mistake. It is so hard to perceive that voice within ourselves. Externally, the political arena is dominated by the mislead, who oppress us.