When Forest of Giant Plants was a thing, the problem was the stadium so it was banned. Grass types weren't banned, you ban the problem. Saying that just because Sylveon GX can be put in the Gardevoir GX deck that Gardevoir GX should be banned is idiotic. I really hate being combative online because I feel civil debate is best especially in these forums but your idea has zero weight to it and you are only complaining because you got beat by it. I play Metagross GX primarily but I do have Gardevior GX and with it I do as well sometimes play Sylveon GX. I too have Plea GX'd a Metagross player and what happened next turn, I got OHKO'd by a Metang with a Choice Band. Suck it up buddy, its not the card, its you.
Are you stupid? I didn't say Sylveon is the reason Gardevoir should be banned. You just choose to assume that because I mention Sylveon. Sylveon is another aspect of the deck but the reason Gardevoir should be banned is because you just slap whatever energies you want onto it and wala! You take out everything in sight aside from maybe Metagross.
I played a guy who dead drew but could only get a Rare Candy onto Ralts with DCE, 2nd Fairy energy, Choice Band, and Field Blower to remove my Fury Belt, he took a knock out on my Turtonator I think it was and yeah, I just didn't have anything set up just yet as it was early in game and he Guzma'ed next turn and it was over. You're saying that's not overpowered? I was powerless to do much about it. I had nothing to do that much damage to it and even if I did, in most games they usually get another one out and just toy with you some more.
I mention Volcanion, Bulu, etc because those are the decks I try but none of them stand up to Gardevoir. And Ninetales? Yeah, I drew Octillery, Remoraid, 3 water energies, DCE, Field Blower. I dead drew but I don't count those as losses. But I didn't want to even try ruining my outlook with Ninetales because I'm down on just about every deck at the moment. Garbotoxin killed my Volcanion and I just couldn't find a Field Blower so I lost. (but let me guess, it's my fault I lost even though I need abilities to win.)