In this instance, The Abyss (Death of Optimus Prime) triggers the Threshhold/beginning of the Transformation (Hot Rod becomes Rodimus Prime). The Hero’s Journey is not about Optimus Prime, but about Hot Rod. I think many fans miss this.
From the perspective of the storyline, I think it’s brilliant, but it upset so many young fans so deeply that Optimus was later resurrected. It set the tone, however– portions of the Monomyth were repeated in G1, Beast Wars, Beast Machines, and later Transformers series.
Till All Are One