I’ve never read Swamp Thing, but in Dangerous Habits John Constantine tells Ellie
What exactly did Constantine do to prevent the Swamp Thing turning into somebody’s compost heap?
Before JC showed up, Swampy just figured he was a sentient plant. JC taught him that he was an elemental power. He also introduced Swampy to the Parliament of Trees.
If that’s not enough, he also allowed Swampy to possess him in order to father Tefe.
He also boosts sales in Swampy’s books.
Off the top of my head, Constantine helped Swampy to realise that instead of just a spirit trapped in a single vegetable body he was in fact an amazingly powerful plant elemental with the ability to control plant matter to a very high degree (from growing a jungle in a city in the space of minutes, to causing a person’s intestinal flora to give him an upset stomach) and move his essence almost instantaneously across huge distances and regrow a body in seconds at the other end.
Constantine took Swampy on a tour of nasty occult stuff happening all around the world in the process of expanding Swampy’s awareness of his abilities, which culminated in his saving the whole of reality.