I've been meaning to bring this up but damn I have a short attention span and end up posting somewhere else and forgetting... What was I talking about again?

Oh yeah, devil fruits.

They can only be eaten by one person, after the first bite it becomes just a regular, disgustingly nasty, fruit. The only exception to this, seemingly, is the zoan type with its models. However I don't think they're the same fruits, just generalized for classification purposes. I.e. the inu inu fruit. Inu Inu no Mi, Model Jackal: Allows the user to turn into a large jackal at will. Eaten by Chaka. Inu Inu Fruit, Model Dachshund: Allows the user to turn into a large Dachshund at will. "Eaten" (more like merged with) by Mr. 4's gun. Inu Inu Fruit, Model Wolf: Allows the user to turn into a wolf. Eaten by Jyabura. All dog dog fruit but different models, and I'm guessing different fruits.
I don't think you're too off with what you have here if you can think up just some different models for all your drakes. Realize its a one bite deal because the "devil" in the fruit enters your body in that bite thus no longer inhabits the fruit to give someone else the same power until the user dies. And so that would also mean you won't grow more powerful by eating more of the fruit, but rather the first captain merely giving into the devil could definitely have the same effect.
And since I'm not all "fix it," and offer up no direction as to how, like a certain boss I know. A few suggestions that may help, feel free to use them as you see fit.
uh... drake drake fruit, Model Bull Drake. Not nearly as fast, but by far the strongest.
drake drake fruit, Model Raptor. The weakest however the most ferocious... and the fastest... that again is the Raptor model is the fast and the furious... perhaps 2 fast, 2 furious... fast and the furious 3 toykyou drift...get where I'm going here?
drake drake fruit, Model fire... not creatively named but this one can breath fire and pretty in the middle with strength and speed. More focused on strength.
drake drake fruit, Model serpent. again in the middle it strength and speed with perhaps more emphasis on speed. It has poison.
drake drake fruit, Model armor. again in the middle it strength and speed it's mostly a defense type with extra hard armor and spiked scales.
Or you can think up your own because to be honest... can't tell the difference between a drake and a wyvern.