The Good:
Similar to the ZCB, Bluemoon Spear, and Zamorakian hasta it has defensive stats which I think is a really cool addition to the game and acknowledges the history of rapier combat, while also acting as a definite successor to the pirate weapons available from Smith. I could see this being a big part of its appeal in the future if defense ever gets reworked or if more content is developed around defense bonuses.
I also see the appeal for PvP as well, especially for pures and as a cheaper alternative to the fang.
Take Away and Suggestions:
The weapon is under tuned and needs an ever-so-slight-buff to occupy the niche is is supposedly designed for which is to be a stab version of the Zombie Axe. The Zombie Axe itself was designed to be competitive with the whip and is the baseline for DPS comparisons. Increasing the strength bonus to match the Zombie axe (+107) would go a long way in making it competitive to the Zombie Axe and the Whip, especially as a Stab and Slash weapon. This would also give it a +1 max hit and put it next to the next max hit break point just like the Zombie Axe. See comparisons here (using both accurate and aggressive styles to demonstrate the max hit break point): https://dps.osrs.wiki?id=AntiqueHorrorEsoteric
Additionally, this slight buff will make the weapon competitive even after you have access to fang, since it will always carry a higher max hit over the Osmumten's Fang, similar to the Zombie axe, which keeps it in the progression longer and will help the weapon maintain longer term value while not power creeping upon the Ghrazi Rapier. Comparisons here: https://dps.osrs.wiki?id=RottenEffigyCarcass
I don't support an accuracy buff, just a strength buff because defenders already buff stab more than slash and crush and running the stab style is a slight accuracy advantage against most monsters.