I think your items and the Pokemon themselves are fine, but the movesets need a bit of upgrading. You don't really need status moves in-game (unless the Pokemon lacks other moves) as just attacking is superior. Also, I don't think you need shadow claw on Empoleon or future sight on Gardevoir. Normally, Pokemon are just fine with one STAB move of each of their types, unless it's having both fly and aerial ace on a flyer. Overall, I would change your team to this if possible:
NOTE: This is designed to speed up the process of defeating the elite four as well as Cynthia herself.
Roserade@Big Root
Ability: Poison Point
Giga Drain
Sludge Bomb
Toxic Spikes
Hyper Beam
Gardevoir@Mind Plate
Ability: Trace
Psychic
Shadow Ball
Thunderbolt
Magical Leaf
Empoleon@Mystic Water
Ability: Torrent
Surf
Ice Beam
Grass Knot
Anything else (maybe return?)
Luxray@Dread Plate
Ability: Intimidate
Thunder Fang
Crunch
Iron Tail
Strength
Staraptor@Razor Claw
Ability: Intimidate
Aerial Ace
Fly
Return
Close Combat
Lucario@Fist Plate
Ability: Inner Focus
Aura Sphere
Flash Cannon
Rock Slide
Thunder Punch
I'd say (for the battle against Cynthia) start with Roserade and try to get some toxic spikes up, just be careful of Spiritomb's psychic. Then do whatever you can with Roserade to defeat the Spiritomb, before switching to Staraptor for Roserade, Luxray for Togekiss, Empoleon for Garchomp (be very careful of earthquake), Gardevoir for Milotic and your Lucario against hers (again, be careful). The Elite Four should be fairly straightforward, but
just in case, I would use:
Staraptor, Lucario, Luxray and Empoleon for Aaron
Roserade, Gardevoir, Staraptor (risky with all those rock types), Lucario (only for her rock types and be very careful) and Empoleon for Bertha
Staraptor, Luxray, Empoleon, Lucario (risky) and Gardevoir for Flint
Everyone for Lucian
Hope I helped!
