supertyranitar-against Raieggs, Gardy relies on top decking Windstorms or Stadiums. If Gardy has one in they hand at all times, then Gardy would have a good match. If not, then Gardy is likely to lose.
Against Metanite, Gardy can tech in Gardevoir Ex (Df) and Crystal Shards to make the match-up easier.
Bandoom is extremly tough, but a possible Sceptile Ex (Cg) tech could help, as could Lati-lock with Latios Ex (Df). Either one will make the match-up significantly easier.
Flariaods is another tough match-up, I will admit that, but Ariados is weak to Gardy, and once again, our friend Sceptile Ex will help, by shutting down Flareons Power.
What I'm trying to say is that Gardevoir will survive and be a good tech in the current format because it's an easy deck to tech into to fit the local metagame. If it wasn't for that fact alone, then it would be bad. Because of this teching ability, it's great.
Alright then.
First off, Windstorm is only half the battle. From what I've seen, RaiEggs doesn't exactly depend on those trainers alone. Plus, with relying on top-decking, it's not always a definite. Not to mention, RaiEggs is just going to be faster. Plus, Raichu d would help alot within the match, with Zzap, and a possible OHKO on Gardy, and most likely will happen.
Second off, vs. MetaNite. Latios* is in there for a very good reason. Not to mention SCEPTILE EX would help a great deal within the match, since, as long as that's out, no imprisoning, which would still allow the MetaNite player to use it's powers, and thus making it a much harder game. Plus, Sceptile ex is a psychic, and can easily rid of Gardy ex d if need be.
As for Bandoom, it'll be hard to get everything set up when the deck itself can set up quick enough, and start hitting things on T2. As true as Lati-Lock can help, the deck still has your weakness, and still sets up fast. So, what do you really use as a main attacker in the match-up? Magneton won't last long, Catty doesn't deliever much, and the only thing that could save you is Latios ex d, and even then that's probably not going to help much due to things like Safeguard Banette, and Shady Move's will rid of it with not too much problem.
And Flariados would be one of it's easier match-ups, of course, even then it's not a guaranteed win. Use Gardy, KO an Ariados. The Flariados player will probably forsake Ariados, and just use Flareon, due to no weakness to Psychic. Plus, don't they usually tech Espeon ex to begin with? And Sceptile ex would help a great deal, yet it is weak to fire/Grass, and Spider Trap can pull things up, can it not?
Gardy will find it hard to survive. Why? Well, sure it can tech, but even techs can only go so far. Plus, it's doubtful it'll be strong enough to take on something like MetaNite, which seems to be the new LBS of the format (With being very strong and all), or some of the fast decks like RaiEggs, or Banette. Not to mention, it's hard to set up compared to something like MetaNite, or RaiEggs, who can take advantage of Castform to full extent. Or Bandoom, which can pull out it's evolved on t2 via Shuppet so long as you have the energy to do so. Plus, Gardy's power makes you take 20 from it's attachments. Sure, it can be resolved via Heal Dance, but that's another bench space. The deck will require alot of bench space to be used, and alot to have out. Heal Dance, at least 1 Catty, at least 1 Magneton, at least 1 Gardevoir PK. Now, with all that, what'll be the attacker, or how is one going to get everything out so fast?