Is there a sword that outperforms it overall or is it the best at everything except for dealing with undead and fiends?
Acheron
The only things that I can think of, off the top of my head, which can keep up and/or surpass an Acheron are Autoguns and Magnuses.
But with the exception of Lockdown, where swing size becomes far more important, I don't think any sword can surpass an Acheron.
I can't log on at the moment so may I ask you a favor? I wanna know whether Acheron deals any damage to Lord Vanaduke in his final phase of the fight. So can you maybe test for me please? Also I want your opinion, do you think Acheron is balanced compared to like the Sealed Sword line and among the other Brandish variants? Or is it just absurdly OP?
I don't have to test it to tell you that, yes, Acheron deals damage to Vanaduke because the normal part of it still deals damage.
All split swords are absurdly powerful. Yes, even that one.
Again, the only reason to use a Sealed Sword over a Brandish is in Lockdown. The hitbox of the first swing on a Brandish is so incredibly small relative to other swords. Theoretically, if you have perfect accuracy and insane reflexes (and/or auto-targeting), then the Acheron is superior to the Gran Faust. However, it's a case of requiring 3x more skill for maybe 1.5x damage.
The thing is that, even before the Acheron buff, the Gran Faust was always a more defensive shadow sword alternative. The current SK meta (which has been stagnating for years now) is all about sacrificing defenses for offenses, especially with CTR boosting Chaos (and Black Kat). Thus a defensive sword that deals less damage in exchange for crowd control and safety is basically irrelevant. Even if we nerfed the Acheron back down to be equal damage to the other Brandishes, it would still be used (or it'll be replaced by the Obsidian Edge), instead of bringing back the GF. Having more DPS is just the final colossal nail in the coffin.
1. no
2. yes