This isn't about viability (though sometimes it can help), it's about common sense.

HG/Y/AS: This six-legged Pokémon is easily capable of transporting an adult in flight. The wings on its tail help it stay balanced.
>can't learn Fly

My 'tism about having to double up on typings in my party is the only thing that keeps me from using Yanmega, or other non-Fly-capable Flying types like Gliscor in-game.