We know Tolkien had a fondnesss of casting his female characters as extremely powerful,
despite putting it down in print that who and who was the greatest. How else would we all think that deep down, Galadriel was far more powerful than Feanor,
greatest of the Noldorin?
Varda, Arien, Melian and Luthien - those ladies mopped the floor with anyone!
As for Varda and Manwe, me thinks their pairing is akin to that of Melian and Thingol, of Beren and Luthien, and of Celebron and Galadriel. The males were in their society deemed the greatest (not so sure about Celeborn), but by what we read of the deeds of their fairer halves, the seems to be a great disparity in the balance of innate power between the couples.
Aiwendil also touched on the seemingly disconnected nature if Varda throughout the books as compared to the pro-activeness of Aule and Ulmo. Perhaps she felt less compassion for life in middle earth as compared to the lesser Valar's? I had the feeling that Varda was contented with the condemnation of the murderous noldrin and infact all life in Beleriand, and was somewhat preoccupied with her time in Valinor. Ulmo on the other hand, perhaps due to his far-reaching elemental nature felt the pains and suffering of the children of Illuvatar more accutely and thus was moved to compassion sooner and acted.
And so we come back to the point of
Greatness. What is greatness? Who was the greatest? Was greatness measured through innate powers and position or through actions that shaped destiny?