Claydol is not a good tank as it has very common weaknesses from ground type: Water, grass and ice. Unless put vs electrical attacker it is a worse option than Grumpig imho.
Mirror coat is better in pvp, Psychic does 100 damage for 70 energy, while mirror coat does 60 for 55. You may not fire off a psychic before getting ko'ed.
Psychic is awful when compared to standart elemental heavy hitters like hydro pump or blizzard, they do 130 damage for 75 energy.