Gyarados DB vs. B

So the Gyarados page states that dragon breath and bite are basically identical. If I understand correctly, dragon breath is rated A whereas bite is rated B (offense) pretty much only because the former is "great" against Dragonite. But who would attack a Dragonite with hydro pump? Wouldn't the advantage of bite against other defenders such as Espeon be (slightly) more valuable? Personally, I wouldn't make a distinction between the two at all.

Edit: If you say DB/HP is great against Dragonite, you may as well say B/HP is great against Exeggutor, Slowbro and Slowking