Presumably Lanham would reject the possibility that the need stems from an inate, or,as many would say, God-given, yearning for justice and moral truth. In this sense, there is not merely "oscillation" between content and form. There is an intimate interconnection. The need to decide, which "drives the system," is born of substantive philosophy and theology.
To use Lanham's example, York in "Richard II" may have been confused about whether he should remain loyal to the king or side with Bolingbroke, but his "need to make a decision" was not born in a vacuum. His need stems from the serious implications of his actions for morality, and for divine and human justice.
Under the divine right doctrine, rebellion against the king was rebellion against God. On the other hand, Richard was an immoral and unjust king, who, inter alia, had exiled Bolingbroke in a seemingly rash and unfair manner, and taken property from Bolingbroke's father's estate in order to finance a hasty and ill-advised campaign in Ireland.
As many commentators have noted, the action in "Richard II" is characterized by elements of fatalism and destiny, as if what is to come has already occurred (as indeed it has) and is thus pre-ordained. York's exclamation signifies that the character in the play understands at some level his need to do something, as his historical counterpart did, and that, it does not matter "what" he, as a free-willing character, might decide, because the decision and the action has already been pre-determined by history. The fatalism of "Richard II" shares something in common Lanham's characterization of the "need to reach a decision" as "[t]he magic moment of transmutation, what drives the system . . . ." Like Lanham's theory, York's declaration, "Somewhat we must do" indicates that something must be done for the sake of the play. Beyond that, it is difficult to say how much York's statement supports Lanham's Strong Defense theory. In the case of Richard II, the need to do something derives from pre-ordination, and, at the same time, from the character's sense of justice and morality. (One may speculate, applying this lesson of "Richard II" to its source, that York's pre-destination was based on the historical York's "need to decide," which, in turn, derived from his sense of pre-destination, justice and morality.) Unlike "Richard II," Lanham offers no explanation of the origin of the "need to decide."
(Incidentally, Lanham overlooks a potentially important distinction between doing and deciding. York's words are "Somewhat we must do." In fact, York's own confusion about the distinction may be significant.)