I get that, but like... I remember back when the UAs for the Xanathar’s Guide subclasses were making the rounds, I voted against the Oath of Treachery Paladin on the basis that we already have the Oathbreaker (as I’m sure many others did). And now I really wish I hadn’t because it never even got a second pass, and it was so much better as a mechanical expression of the concept of a Paladin who violated their Oath (as opposed to a Paladin sworn to an oath of evil, which is what the “Oathbreaker” seems like).
Also, despite the similar names, I feel like the Undead has a distinct story identity from the Undying. The latter feels like a lich in training - someone who made a pact with an undying being to extend their own life beyond its natural limits, while the former feels like someone who made a pact with a being that wields power over undeath for a measure of that power. Like the difference between giving your eye and hand to Vecna in exchange for the secret of lichdom vs giving your soul to Orcus in exchange for the power to wake the dead.