No the word quintessential is not a noun. It is an adjective.

The quintessential ingredient in cake is flour.

Quintessential Vocal Ensemble was created in 1993.

Her comportment throughout the ordeal displayed a quintessential bravery.

"Quintessential" is an adjective that describes the perfect example of a particular type, The quintessential quarterback would be one who has all of the traits and qualities those who are knowledgeable about football would expect from a quarterback. There are quintessential villains and heroes. It could be that "quintessential" is generally used to describe people, but that may not be necessarily true.