Gardevoir

At first glance, Mega Gardevoir seems to be a solid wallbreaker, tearing apart bulkier teams with its high powered STAB attacks, as well as shutting down walls such as Chansey, Slowking, and Blissey with Taunt, thereby easily breezing past common defensive cores. However, Mega Gardevoir is thoroughly outclassed by Tapu Lele as a wallbreaker. Tapu Lele is much more useful in matchups outside of bulky teams while still maintaining the ability to tear down balance teams, has the ability to hold items to further increase its power, and boasts a stronger Psychic-type STAB attack under Psychic Terrain. Mega Gardevoir also is unable to outperform Clefable, Reuniclus, Tapu Fini, or Mega Latias as a Fairy- or Psychic-type Calm Mind sweeper, due to their respective individual advantages over it such as an immunity to damage from status, access to recovery options, or better bulk. There is generally no reason to use Mega Gardevoir over Tapu Lele or any of the aforementioned Pokemon at any time, as even the slight Speed tier increase isn’t worth it.