Procedural legitimacy is justified in two dimensions. The first is that a stable society follows from everyone inhabing their role, or playing within their understanding of the game. The second, perhaps unique to liberal democracy (or perhaps more general), is that in the determinations of the several roles and the game-playing, a sufficient number of ideas is created to give people an understanding of the event. There must be sufficient freedom and understanding constituting the exercise of power so that the objects of the power can identify the freedom of the lawgiver with the freedom of the subject. In a free and equal society, this provides the basis for the lawgiver's freedom. One must exercise power to preserve sufficient freedom for the exercise of power.
When the ways of thinking about power change, they don't so much augur political change, as make it a logical necessity. The building falls because the nature of gravity has changed.