Yes. Gardevoir should almost never use EVs in Defence - at least in competitive battles. It has better things to spend EVs on.
Even with full EV investment, perfect Defence IVs and a positive nature, Gardevoir reaches a disappointing Defence stat of 251, which is easily overpowered by the many physical attackers in the game. Gardevoir should only be interested in using HP and SAtk EVs, and if using the Gardevoirite, Speed instead of HP. There is nearly no situation where Defence EVs would help, since the end result is disappointing and you could be using the EVs on a stat where they'd actually help.
You can use a teammate to cover for Gardevoir's bad Defence stat. Some examples include Skarmory and Ferrothorn, who can both effectively take physical hits and take Steel and Poison hits for Gardevoir.
Since Gardevoir is Modest, it would be wise to max its Special Attack to ensure it hits hard, and use a mix of HP and SDef if you aren't using the Gardevoirite. Otherwise, Gardevoir should run max Speed, since it needs to outspeed as much as it can, and base 100 Speed is useable unlike regular Gardevoir's 80. In fact, it would be ideal to run Timid for this reason, but since Gardevoir is Modest that is out of the question.
