quintessential, isn't it? The Fifth Essence, the Fifth Element, Quintessence is quite possibly the force making the universe accelerate, or perhaps it is the antithesis of Dark Matter? Is it an alchymistically condensed and refined, purified distillate of Luminiferous Aether? Does it have something to do with Vacuum Energy or Zero Point Energy? Physics has been very fickle in its love-hate trash it/keep it/rehabilitate it relationship to Quintessence. But that's science for you--always rushing after the latest fad and quick to distance itself from its old friends and pack away the old toys so no one notices them.
But Alchemy never forgot Quintessence. Alchemy is not a game, but rather a tool, a process, and an aspect of Natural Philosophy that was, much like Aether and Quintessence, relegated to the dust-bin next to Astrology, Geomancy and the Doctrine of Signatures.
Quintessence? It never went away. How could it? It's the purest, most perfect essential state of any matter and even if we call it a dozen other names or concoct elaborate mathematics to hide our shame in referring back to concepts bandied about by dodgy old guys with funny little furnaces and an inordinate amount of exotic glassware, so what? Quintessence remains pure, unsullied and rich in potentials and possibilities that have barely been tapped.
An Alchymist develops Quintessence as one of their core endeavors. It is incredibly useful, and is an essential part of developing Philospher Stones, Serums, Sirrups, and other wondrous concoctions, decoctions or distillations that cure ailments, improve performance, and produce incredible effects.
You could say that Quintessence is at the very core of Alchymistry.
But there's no need to blame Paracelsus.