I was just wondering this since gyarados's best attacks through level up are special attacks like hydro pump, hurricane and hyper beam, but gyarados's special attack stat is really bad. Why don't they just give it waterfall or giga impact or something? I know it hyper beam used to be physical in gen 1-3 but that still doesn't explain about hydro pump and hurricane.
Nobody really knows the answer except for Game Freak. If I had to take a guess though, most water type moves are special. Besides, Gyarados gets STAB from these attack anyways. Also keep in mind that in the first generation (when Gyarados was introduced) there was no special attack stat. Special attack and special defense were one stat called "special". In generation 2, the special stat was split in half into special attack and special defense. So Gyarados was more powerful in the first generation than it is now.