[X] Enlightenment's Unbreaking Mirror: B
When you get right down to it?
Narratively, Thousand Year Impenetrable Mist does nothing that we can't already do with our own Arts. It's ideal for protecting the weak against grossly overwhelming power, but does little for those who are already strong, or against those who we can guard against with other techniques. It's basically just one more "Group Soak" effect that Ling Qi can throw out on a whim. More importantly, it does nothing to actually remove the targets from the dangerous position, because the enemy is still capable of attacking again if need be. The range is limited by [The Mist] and its borders, and the circumstances in which we can't employ EUM but could deploy TYIM requires some extremely torturous logic or the employment of enemy hyper elites to stomp on us in particular (And that problem would not be solved by making them have to double tap us instead of just dunk on us in the first shot.)
EUM meanwhile? It gives us a table-turner. Ling Qi draws an incredible amount of aggression on her simply by what she represents--a field of overlapping field effects that promises victory for her side as long as she's able to remain present. We've seen in virtually every major fight that she draws a stupid amount of fire, with Zhengui taking second place by dint of the Distraction Carnifex element of being a giant snake-tortoise. At any point during this, she can activate EUM and drag everyone down into a confused mess as their malice is turned back on them and their senses severed with the blade of night. During this window? She can reposition her friends, her allies, or launch attacks against reduced defenses because they can barely detect what the fuck is going on. It has presence in a fight--and more importantly, the secondary effect is generally better for the small, elite groups that Ling Qi tends to be deployed along with. The math clearly establishing that EUM is generally superior for Third Realms who didn't completely dumpstat their conditioning and all, even if it lacks the damage floor that guarantees people survive the initial hit.
In the end though, what it boils down to is that I want our Domain Techniques to be special, to do things we can't necessarily get on our own. TYIM is good--and when it's at it's best--you really want to have it. But it occupies the same narrative space that moves like Black Mirror does--a group defense that turns a big attack into something that hurts nobody. Doubling down on this can have a valuable impact, but in the end it would feel like something we almost never get to see because our own arts are generally superior.
What we lack is a real table turner if we're pressed--and EUM fits that to a T.