Well, Nimbus forces a duo and it has a greater upkeep...
The 2 point upkeep definitely helps balancing a bit, but consider:
6 nimbus
6 quint
about 3-6 support cards
Water mark, air and aether pendulums to fill out to 30-35 cards ( just pillars if used as an arena deck)
Its a trio, so there will be some quanta instability there, but essentially you can have a nearly unstoppable permanent creature silence in effect... Thats a little too powerful.
In fact, just add in silences and you can make is so that your side will be the only one that can cast creatures...
e.g. use deluge till silence drawn
play silence and let deluge wear off
play creatures next turn (opponent wont be able to do the same)
turn deluge back on.
End result is opponent's creature production is fully locked down.
Quintescence means the only recourse is shields... This can always be overcome using SoW though.
That deck would get old REAL fast.
