Five really big things that could make this weapon worth the titanite Scales it currently is undeserving of:
1.) Lower the magic base damage of this weapon to 26. And then add the amount lowered from magic to the physical base damage (52 + 78 = 130). Having an even split with shoddy scaling diminishes the effective damage of this weapon entirely.
2.) The INT scaling is low enough (D), so the DEX scaling could be raised back to an A again. This is a weapon wielding by an expert assassin after all, so the DEX scaling should reflect the skill put into it.
3.) Increase the critical to 105. Once again, it is a weapon used be an expert assassin.
4.) Have the weapon skill Crescent Blade scale off the total AR of the weapon.
5.) Increase the activation speed of Crescent Blade.
There, now you have a weapon that uses boss-tier upgrading path, requires the completion of a questline spanning mid-to-late game AFTER killing a certain Lord of Cinder (more if you choose late game in order to not fail Sirrus's questline), and be worth it all!