Now I see your point, and overall on the Lightbringers I agree. Indeed they don't fit with the powers they display at the moment.
On Angmar, while I see your point I personally don't share it. I'd still see it better as adapted to the others and fitting in in all aspects than having it go 'Yolo' with the excuse of it being fictional. Don't mean to sound offensive, just my thoughts.
Now, back to lightbringers:if we keep them, perhaps we could still have them as a supporting unit, and with an elemental twist, only more passive and, to use Tolkien's words, Unseen. They may have studied the ways of the Elements, but in a 'spiritual' way, not unlike what we see from the Three Rings.
Let me explain:
This idea would see the Lightbringers as something of a cross between Orc Overseers and Elven Chanters. When produced, they are pure white, and technically speaking not unlike the scholars, but they can be made to join a troop of unit, and then unlock a selected power they have studied:
-Fire makes the spirits of the unit burn with unstoppable will, increasing their damage
-Water blesses the troops with the light touch of running water, gaining a passive heal when not fighting
-Earth awakens stony resolve into troops, whose armor values increase
-Wind makes the units run on the winds, increasing movement speed
Of course none of these abilities would be strong enough to hold a candle to the powers of the Three, and a single Lightbringer may unlock only one.
An alternative would be to have them run freely as single units, and have all the elemental powers available to make an aura that has the same effect listed above, only temporary and needing to cooldown after use.
I propose this just because, while out of place, I can quite see Elves in tune with the forces of nature, and after seeing the effects of the Rings, perhaps this support role would be acceptable. Not exagerated, and more spiritual than actually magical, it could be more fitting.