It is indeed a rather pointless sword. Prior to the first arsenal expansion, the only upgrade available the Brandish was the Cautery Sword. So back then it was a slight step up in damage plus a bonus to slimes.

With the inclusion of the Nightblade, the Cautery sword is suddenly obsolete. The Nightblade's inherent shadow damage bonus to slimes is much better than anything the Cautery sword could hope to muster. Sadly the Cautery sword is still there, luring new knights who want to do more damage to slimes. The worst thing about the sword is that it is a deadend unlike the Nightblade that goes all the way to 5*.

The WORST part of the item isn't that it doesn't have any upgrades (if I'm running through an earlier stratum I might get out the ol' wrench wand just for fun) the WORST part is that, comparitive weakness aside, it's also a very simple and boring weapon.

Basic basic attacks and a charged attack that's just a single basic swing at higher damage. Boooooooring.

I like the weapon's model, though. I wouldn't mind if they'd get rid of this sword and then reuse the model for something else..

Or heck, maybe they could add some kind of special functionality to all inherent-specific-monster-bonus weapons that a UV on any other weapon couldn't match. Like, what if killing slimes with a cautery sword (or beasts with a hunting blade, or constructs with a deconstructor, etc. etc.) offered a notably improved chance of finding rarer loot? Or a chance at special loot that would not drop in any other situation? Would some folks be tempted to carry notably inferior weaponry if it had some kind of special loot farming capabilities? I might.