Hello everyone. I am currently facing Terra and personally I think this is arguably the toughest gym leader that Ive faced so far. I managed to get through here cheap Quagsire but when I get to garchomp, even when I get him to minus 6 from spamming Draco Meteor, is still able to oneshot me at minus 6 special attack. I also do not understand how she can have a level 78 when we are capped at 75. Below is my current team and their sets. Any help will be greatly appreciated. Yes I know I should probably get rid of Magneton but I am able to take down quasire with it since Quagsire looses its ground typing due to the telluric seed.
Tangrowth 72 Giga drain, Power Whip, Knock off, Ancient power (Rose Incense)
Infernape 72 Close Combat, Flare Blitz, Mach Punch and Shadow Claw (Charcoal)
Swanna 72 Hurricane, Surf, Air Slash, Tailwind (Wave Incense)
Magneton 72 Charge Beam, Discharge, Flash Cannon, Tri Attack (Zap Plate)
Pilosand 73 Shadow Ball, Giga Drain, Earth Power, Shore Up (Spell tag or earth plate) I alternate between the two
Meowstic male 73 Psychic, Psyshock, Disarming Voice, Rain Dance (Twisted spoon)