The most annoying misconception that people have of Poseidon is that he is only a “Sea God” and therefore less important than the other Olympian or Chthonic Theoi of the Hellenes.
He is the Earth-Shaker, something very important in a tectonically and volcanically active area like the Mediterranean basin. He is the Father of Horses, who GAVE humanity the gift of the horse, something that links him to the land in ways that people don’t expect. He is a god that can help PURIFY with his waters.
These are all things that trivializing him into “The God of the Sea” ignores.