I agree that the difference in power between a Maia or even half-Maia and an Elda is probably more significant than most people seem to think. And besides, the Elves of the Third Age needed Rings to reach that kind of power whereas the Maiar.. well.. ended up with Rings also.
A few of them. But I think my point still stands.
And anyway, Lúthien's already beaten Galadriel to the Most-Joy-and-Most-Sorrow thing, and the Only-One-to-Ever-Move-Mandos thing...