My guess on the new Dragons:
Fire Dragons are going to be too OP, a little too much, mainly because Riot is doing it wrong (they want to make trades against heroes stronger).
8%/16%/24% bonus AD-AP is a little too good compared to the other bonuses, and this goes further when you consider that it's goal is to make you better at trading against champs: NOPE, it makes you better at trading against anyone: champs, monsters, towers, and poros.
If Riot actually wants to make it improve trades against champs make it increase the % damage against champs.
Also they will need to improve the effect of the
Wind Dragon: make it add % speed out of battle and HALf of that amount during battle.
Water Dragon: make it increase all healing and regeneration effects at % (half while in battle).