Luthien weilding Vilya

[Zigûr]

To look at it in terms of the stature of their Enemies rather than the wielders themselves, I can't help but feel that no Elven-Ring would have made any realm in Beleriand impregnable to the Hosts of Morgoth. Morgoth may have been frustrated had he attacked a Ring-wielder in person, mind you, but I feel as if the Elves could not have resisted indefinitely dragons and Balrogs in any significant numbers.

Sauron could only have successfully assailed Lothlórien had he come there himself; but we know that in terms of power Sauron was, in a sense, the opposite of Morgoth: with both in a weakened state (Morgoth at the end of the First Age, Sauron at the end of the Third), Sauron was more powerful in person than indirectly (due to his power being largely invested in the Ring, which he lacked) while Morgoth was more powerful 'by proxy' than in person, which is to say that by that point his powerful armies and servants were more dangerous than he was as an individual, because his power was invested in the world as a whole and everything in it, and especially the most powerful of his forces. Sauron's power was concentrated, Morgoth's diffuse. I think that may have a part to play in understanding how an attack by Morgoth's armies might deal with an Elven Ring.

As an aside, it's interesting to note that in some early jotting by the Professor (as recounted in The Return of the Shadow, possibly?) he mused on an origin where the Rings were forged by Fëanor in Aman and were part of the stash of goodies Morgoth stole from Formenos - so this discussion is not an unprecedented notion!