Gardevoir has serious competition with the new Psychic Fairy on the block, Hatterene... and is found wanting for the most part. Gardevoir is a series of not enoughs. Not enough Speed to sweep, not enough Offense to wallbreak, not enough defenses to wall. Gardevoir pales in comparison to Hatterene, whose stats are more focused into a Bulky Slow attacker, combined with Trick Room to support those tendencies and Magic Bounce to ensure that Trick Room gets up.
Gardevoir's main claim to fame is unpredictability. Gardevoir has a wide support movepool with numerous ways of disrupting opponents (Will-o-Wisp, Thunderwave, Toxic*, Trick) as well as plenty of buffing techniques (Heal Bell*, Dual Screens, Calm Mind, Healing Wish) along with a wide range of attack options, meaning it is very difficult to counter all Gardevoir variants.