I think the root of this problem is that infernal dragon is too powerful and ocean is too niche. Ocean is great on champions who have either mana or health sustain problems but worthless if you don't (Ocean drake is hilariously useless for champions like Garen, WW or Xin), while all the other dragons provide buffs that are universally useful.
My solution is therefore as follows: keep the RNG (it keeps games fresh and it requires you to adapt, which is an important skill to have in League), nerf infernal drake back in line and design a new, universally useful buff for ocean drake.
As a complete aside, air drake can have plenty of offensive applications as well. When I'm playing Rek'Sai for example I prefer air drake even above infernal drake.