Gyarados and Golduck are literally the only two that need that.
I don't see why you're handing Dragon out to any Pokemon that asks.
Cloyster and Blastoise as steel doesn't even make sense.
Sceptile learns dragon moves. It is a lizard just like Charmeleon who turns into Charizard (allegedly a dragon).
Yanmega is more dragon by species name then attacks, though we don't have a bug/dragon and too many bug/flying types, so why not try to reinvent the pokemon a bit for originality?
Please tell me hoe Cloyster and Blastoise don't make much sense. I kind of see what you mean, but I'd like to know the evidence behind it. The reason I made these types this way is because of Cloyster's shell being protective (I didn't realize he was water/ice so he's probably a no) and Blastoise's blasters (and the fact that Blastoise can learn some steel moves).