[Poetry is, like all art, something that takes on new life in the face of each person who interacts with it, based on each individual's life experiences. There are many ways to interpret art, though it is—in my mind—almost impossible to say one interpretation is "the only" interpretation. The following is from research, as well as my own personal interpretations.]
In Shelley's "The Triumph of Life," lines 211-247, I did not find any similes. However, I can provide an overview of what Shelley seems to be saying in this segment of the poem.
Shelley begins this section referring to the great ones who have come before: leaders of the church, military and kingdoms, intellectuals ("mitres, helms, crowns, and haloed sages"). Shelley believes that with all the knowledge these great individuals were given, they were never instructed in the art: "to know themselves."
These great ones hid their ideas as one would hide mutinous thoughts (thoughts that did not conform to the popular view) under the cover of darkness (perhaps symbolizing the lack of knowledge), rather than out in plain sight (the light, symbolic of knowledge or enlightenment).
Shelley refers to the French writer and philosopher Rousseau, who though not a contemporary of Shelley's, had an enormous effect upon the world and how "men" thought. Regarding "The Child of the fierce hour:"
The sparks of Rousseau’s writings had kindled a thousand signal fires—including that of the French Revolution, of which one child was Napoleon, who is described in lines 215–27.
Shelley seems to feel that powerful "intellects" have crippled the world, hindering advancement—enabling anarchists to rise, while hampering great minds:
Presumably Voltaire (the immensely influential thinker of the 18th-century Enlightenment) is the “dem- agogue.” Frederick the Great of Prussia, Catherine the Great of Russia, and Leopold II of the Holy Roman Empire, all influenced by Voltaire’s ideas, are the “anarchs” (leaders who bring about anarchy). Immanual Kant (the great philosopher of the German Enlightenment) is the “sage.”
Overall, at the end of the passage, Shelley seems to indicate that the passionate nature and ideas of Rousseau prohibited the philosopher from ever being truly happy, as he strove toward impossible ideals. My sense is that Shelley, after the time of Rousseau and other "influential minds," looks not to the significance or prominence that may have been "falsely" attributed to those who followed them, but those who came before—"the old faded"—who one might believe knew a truth that has been obscured from the world.