I love using the enemies cards for your advantage (played "fishing" deck back in MTG
)
i have difficulties deciding elemental belongings, so thats free to discuss.
On another note:
There are so many good card ideas trying to create synergy between elements, but fail cause of rainbow usage.
Why not creating cards having requirements to play, for example "Can only be played if you control 2 or more different no neutral pillars."
This should not be an overall use to obtain synergy, but could be a series insteed.