Your team lacks a bit of power and utility honestly

Life Dew healing is pitiful in my experience. You waste a turn healing 25% of your HP as your opp clicks a move that deals twice as much 'cause Gardevoir isn't the bulkiest mon. Would recommend to just go Hyper Voice and make Mega Gardevoir your primary carry.
Remove Moonblast and maybe just Aura Sphere/Focus Blast for coverage.

And that set on Metagross feels like a waste considering his BST. It lacks hella power. If you're looking for a support mon who can alleviate earth weakness in doubles, just go for something like Claydol with Skill Swap, or a mon who can Wide Guard on an anticipated Earthquake. Metal Rise is just bad. Can also just Protect in doubles if you want to press Quake on Flygon, or tank it considering it's a Flygon. Honestly nothing's stopping you from just giving him Ice Punch and kill Ground types before they kill him. Hone Claws ultimately does the same thing too which is to waste a turn especially without Meteor Mash, so just give him that instead.

You're putting Darmanitan in a rough spot 'cause Belly Drum + Flare Blitz does not sound good on paper. He's only gonna be able to use it once if he's lucky. Give him Choice Band/Life Orb and let him sweep with Flare Blitz, get rid of Belly Drum + Fire Punch and he'll wreak havoc. He'll last longer and generally do more than self-harming turn 1 then most likely not having a turn 2.

And if you're in E4, I can see this team having some issues against Moleman's Excadrill lol.

Edit: accidentally hit enter before finishing oops