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Gyarados isn't bad, but there's always been one thing about it that bothers me: the Flying typing. It doesn't make too much sense thematically, but it also seems to exist solely to as a handicap. It makes it even weaker to Electric, weak to Covert Cobblestones, and doesn't provide useful STAB. It only learns three (3) Flying moves: Bounce, Hurricane, and Hidden Power. Two of those are special, which Gyarados will never use, and the other is a two-turn move that isn't Geomancy or Solar Beam, so nobody gives a shit about it.
I think Water/Dragon is the way to go. Not only is it an incredible defensive type, it makes sense thematically as well, since something based on a Chinese dragon should be, well, a dragon. Pure Water also works. I do realize both of these would make it lose the Ground immunity, but I think it's a decent tradeoff.