Will to Power and Weakness of the Will

Nietzsche's model, presented in #19 of Beyond Good and Evil, of the hierarchical individual soul, is, of course, derived from Plato and Aristotle, and is implicit in Kant's concept of Action, as well.  Hence, he also inherits the problem of 'Weakness of the Will'.  Now, whereas Aristotle explains the latter as a deficiency of knowledge, thereby entailing that the 'lower' soul always conforms to the dictates of the upper, Kant allows that 'Evil' can insinuate itself between Reason and Inclination, and, so, can lead the latter astray.  In contrast with both, Nietzsche's theory of the Will to Power seems, in general, to imply that 'weakness' connotes a relative deficiency of 'strength'.  Accordingly, any act of disobedience must be constituted by an increase in strength on the part of a hitherto weaker entity, with respect to a previously stronger one that had been controlling it.  But, if so, then, by implication, any act of 'obedience' is adequately explained as the mechanical consequence of the stronger overpowering the weaker.  Thus, if Nietzsche had applied, as he does in #36 of BGE, Occam's Razor, to his analysis in #19, he might have dispensed entirely with his conclusion that the 'obedient undersoul' is "happy".