However, I see no reason why Gyarados was given the Flying type and we all have experienced the crippling state he has to face against Electric types. I feel he would be overall better as pure Water, or maybe Dragon if it comes to that. Not a bad option either, Outrage is a physical Dragon type move enough for Gyarados.
From what I hear, Gyarados wasn't made Water/Dragon because it would have made him insanely overpowered back in Gen 1. I suppose the Flying type was assigned as both a way to nerf him as well as having some semblance of similarity to Dragon by pure aesthetics (wind/storm/cyclones are often associated with deities/mythical creatures in ancient cultures).