Note that it clarifies when mega forms are included. For Pokemon that are viable even without their mega forms, it's listed like this: "Gyarados / Gyarados (Mega)", complete with sprites for each. For Pokemon that depend on their mega to be viable, it's "Pinsir (Mega)", with a lone sprite. As you can see, the formatting used implies that many people consider regular Gardevoir absolutely viable. Don't mean to make it sound like what Smogon says is necessarily the word of god, but they usually know what they're talking about.
It's still in the works, but it's more complete than the last time I mentioned it.