First and foremost, thank you all for the meaningful support shown. I'll update the main post and insert your name in the 'in favour' list.
I like Samsara's addition related to knock-back immunity. I feel it stresses Vilya's influence on heroes even more. Hence, at the present day, here is the final rendition we have agreed on:
Level 10: Vilya's Preservation - The mightiest of the Three Rings shields Middle-earth from evil and toil. All allied buildings and heroes across the map gain +50% armour and are immune to magic. Heroes cannot be knocked back and their abilities recharge much faster.
Lasts for a long duration.
Some remarks on the text: I replaced 'Rivendell' with 'Middle-earth', so to indicate that Vilya operates for all the forces of the Good, and we also reconnect with our own interpretation that wants the Ring to maintain a minimum amount of order in the world.
All in all, we've done an Elf's job in characterising each of the Three as it was due. Vilya and Nenya will provide a true, global shield, while Narya shall relieve its bearer's shoulders from the burden of his mission; additionally, may I conclude, not only does the Ring of Fire ensure an adequate balance between the wizard's bubble-shield and magic efficacy, but its main focus lies in resistance to adversities, such as ice, fire and poison (the adversities of Gandalf's numerous journeys). Well done, astonishing work!
P.S. Samsara, I noticed that your name is missing from the Narya concept's list. I assume you have by now accepted the entirety of the proposal. Give me a confirmation and I will add your contribution, too