The 4 elemental dragons are signature cards. They should be “dragons of one of the most powerful cards of their element”. The other 3 Dragons usually grant huge benefits to the player. Therefore, why should the water dragon be the exception? It often gives you very little benefit due to a large amount of cards have powerful gift effect and inferior stats to the point the water dragon might sometimes even nerf your creatures. Therefore, why not grant “all transform creatures +2/+2” as a fail safe and move the water dragon on par with the other 3 dragons?
BTW, if this card gives you the impression of “even if it grants +2/+2, I still wouldn’t run it” it will just show you how messed up terrible that card is, more so with the fact of it without the +2/+2.
I think the blue dragon is far closer to being constructed playable than the yellow dragon. Blue dragons effect is actually very powerful, it’s just win-more. Your solution doesn’t fix this problem, it makes the card even-more-win-more.
If you really want it to be playable, you need to basically redesign it completely. Some potential redesigns.
Ascendancy maintains the random transform aspect of Orosei’s mechanical identity but focuses the effect so you can get value when you only control orosei and a single other creature. Willpower maintains the “go wide” aspect of Orosei’s mechanical identity but does so in a way that’s more controlled and more value. It might need to say “Gain 3f for…” in order for it to actually be good enough though.
It could also be a weaker Auroras Dream effect such as, “Draw until you have X cards, reduce the cost of all cards in your hand by Y”.