So you say that the only useful drake is the Infernal one? Then sir, you haven't witnessed how efficient split pushing can be with if you have Mountain Drake buff, or how much sustain an Ocean Drake buff can give you. Heck, even the movement speed boost from the Cloud Drake buff helps junglers and assassins roam.
I can't tell you enough on how many times an Ocean Drake buff has helped me sustain through losing match-ups in any lane or even sustain while jungling, how convenient roaming can get with a Cloud Drake buff or how pushing lanes and taking objectives becomes much faster when you have a Mountain Drake buff.
I'm pretty sure everyone agrees that all drakes have some kind of use and that the Infernal Drake isn't the only drake that's useful.