As it is now, every Empyrean is essentially the same weapon.
Build TP to 100, 200, 300, get an identical aftermath. There aren't anything that focuses on job abilities or traits, like mythics, and there's no great special effect, like on relics (Increases critical hits on Ragnarok, Enhances counter on Spharai, Amano's ability to weaken attacks, etc.)
That being said, I think it would add uniqueness to Empyrean weapons giving each of them its own specific special quality to separate them from one another. DMG wise, they're in the middle of relics and mythics and on each end of that, you have enhancing qualities to either job abilities or the weapon itself.
Empyrean weapons should also have this.