Trophy Pokemon. Fighting and psychic moves have no SE overlap so there's not really a niche that this Starmie would excel in, and Starmies don't make good defenders either - low stamina and max CP.
On Starmie you pretty much only want Water Gun + Hydro Pump or Psychic. Hidden Power is a weak move on offense, on paper being on par with Water Gun which makes it worse in actual usage, being less dodge friendly and because you do more damage spamming many low damage quick moves rather than one high damage slow move.
