Lemme just say a quick thing. Magearna is fun if you're the one using it, but it complete pain in the donkey to face. It's bulky, has insane special attack (further boosted by soul heart), defensively crazy, and has a slow volt switch. If it could have air balloon/levitate without losing what it already has, it would be busted to hell. Assault vest allows it to pivot and wallbreak well. Life orb and shift gear allows you to sweep quite easily assuming things like chansey aren't there.
The biggest things stopping gear witch are faster, crazy good physical attackers with SE hits (e.g. exca, though it would die to an aura sphere) and forcing it out and in on entry hazards. Spikes are a boon if you can get them up. Burning it helps with chip damage, but even then it doesn't die easily.
So yeah, fun mon if you're using it. Definitely give it a shot.