Will to Power, Obedience, Slave Rebellion

According to #19 of Beyond Good and Evil, a "well-constructed and happy commonwealth" is constituted by relations of mutually satisfied Commanding and Obedience, that express comparative degrees of strength.  Now, in #195, Nietzsche refers to the "beginning of the slave rebellion in morals", a concept that he later develops into a 'genealogy of morals' based on the difference between "master" Morality and "slave" Morality.  However, there is a profound lacuna in this genealogy as derived--the transition of an underclass from a happy to a dissatisfied condition.  For rebellion cannot occur so long as the mutually satisfactory comparative degrees of strength are maintained, so its occurrence presupposes that the power relation has already shifted, in which case the erstwhile Obeyers are already no longer 'slaves'.  In other words, the Will to Power, at least as elucidated in passages such as #19, does not sufficiently ground both a Will to Obey and a Will to Disobey.