Zoroark GX is a very consistent, but Sylveon GX is even moreso. Magical Ribbon just straight up guarantees how your game will progress, and swinging for 110/140 choice banded is a 2 hit KO on anything in the game. I'm actually very looking forward to playtesting Gardy/Sylveon/Zoroark vs. Naganadel/Stakataka, because despite the fairy vs steel match up, I think it's still a winnable encounter.
The match up is in Naganadel favor, it is a faster deck (there is no way that it doesn't hit at least 110 turn 2) and steel weakness is hard to deal with. Sylveon has potential after rotation because it will be one of the most consistent deck, but it needs a ohko attacker in the form of a basic, otherwise it can't keep up the pace of naga/taka or other faster deck such as malamar, vikabulu, buzzwole etc.