Vaporeon completely walls that.Here is why HP Dragon is dumb: Suppose you are using it on other waters. A torrent boosted, STAB resisted surf gets 95*1.5*1.5*.5=107BP, like someone said before. HP Dragon gets...70. Surf hits harder. Ice Beam is vastly superior against all dragons except for Kingdra (well, and Palkia, if you want to go there). There is no pokemon you can outdamage by the Surf-HP Dragon combination than with the Surf-Ice Beam combination besides Kingdra. Any look at this: Kingdra often only carries attacks that come with the water, dragon typings! No one is going to try to take down Empoleon with a Kingdra, because that is counter-productive. So, to conclude, HP Dragon is much less viable than Ice Beam.
And HP Dragon would be 70*1.5 from Petaya which is actually 105 BP, not
As for Kingdra...Assuming you have Petaya/Torrent active, a Waterfall/Outrage will still kill you because you will be so low. I agree that Kingdra does do nearly nothing to you, but after Petaya and Torrent that is all you really need.
But I see the point of what you say, and what others have said, I was just thinking it could surprise some people, and give you that slight advantage early. Lets just drop it then, and discuss some other set.