Gunbreaker vs. Dark Knight

[Absimiliard]

You've both pretty much hit the nail on the head.

The explosive force and vibrations produced by gunblades would probably shred any normal armor. And even should the dark knight have armor that will hold up, concussive force isn't the easiest thing in the world to stop. Just being bludgeoned by a hammer would cause catastrophic injury to a man in armor, so we can only guess at the sort of trauma one could expect from such powerful explosions being released in such close proximity. This is worsened when one considers that there really isn't anything stopping a gunbreaker from whipping out an actual sidearm with their free hand and just straight capping somebody. I believe there's even a gun holstered on their AF gear, isn't there? On the other hand, the way dark knights use aether so extensively in their attacks (not to mention how massive their weapons typically are) might actually give them the advantage in destructive power.

My thinking is that a gunbreaker could end the fight very quickly if they managed to avoid the dark knight's first strike and capitalize on the opening provided by swinging such a huge weapon around. I would argue that there are numerous means of countering this, but all such arguments are made exceptionally difficult by the sheer size and weight of the weapons dark knights wield. I will say, however, that it may not be so cut and dry if dark knight is capable of manipulating aether into configurations other than what we see in-game. The raw power of their aether-based skills could potentially turn them into a truly horrific opponent in the event that they are more versatile in story than what game mechanics show.

tl;dr: My opinion is that gunbreaker wins if it can get in fast and hit hard. Dark Knight's chances of winning begin to rise if the gunbreaker fails to take advantage of the first opening.