Those who existed before creation may believe they will exist after it, free from pesky restraints like linear time.
No one may have usurped TWG .....yet. Lucifer has clearly been trying since the Fall but unsuccessfully. Similarly the Outsiders have been trying to get in for the same period. Lucifer has had the Denarians in operation for the last three full cycles, but they have failed to make headway, hence this cycle he has switched it up with the Black Council.
The body that was Drakul was born before 1395 which put it slightly off for a Starborn, but hey poor record keeping, he could have been born earlier but not aged, but means he is challenging for the first time this cycle, at least in this form.
What is changing is the guardians of the Gates. When the Denarians rose it would still have been the Roman/Greek Gods, they would have given way in the subsequent cycle to Winter, this cycle may be Winters last giving way to humanity as the guardians of the Gates, if so could this presage an end to the challenge through the cycles? Cementing the White God permanently? With humanity too numerous to be extinguished?
By the next cycle humanity may have spread to the stars escaping Earth under its own power creating the Singularity, or as we know him The White God. That would close the circle on creation and shut the Outsiders out permanently, leaving whoever is sitting in the White God’s chair as the White God, it’s current incumbent, Lucifer or Drakul. Maybe it’s a three way battle Uriel, Lucifer And Drakul to become The White God. Two Archangels and what?
The monster that Drakul was before Drakul may have been the biblical Leviathan, a being of both chaos and envy, and which has appeared under different names throughout history (Tiamat, Jorgamundr) It would certainly fit with WOJ on Drakul. Leviathan is oft portrayed as a dragon from the sea. Leviathan forces themself into a Starborn body which has the potential via a Darkhallow inhaling the Outsiders to reach Archangel level just at the time when the White God is about to come into existence.
Except, by entering Creation they are no longer entirely free of linear time. They are less restricted than mortals by it, but their influence is less than mortals too, so it balances out. I doubt Ethniu thought she could be defeated or even killed (although I am sure she is aware of the immortal-killing conjunctions such as Halloween, all of the immortals would be particularly as their is significant advantage too...they get to be mortal for a day and influence things a bit - high risk, high reward). But she would be mad truly to think that just because she pre-dated Creation she would always exist. We know that just isn't the case for immortals. None (except perhaps TWG) are invincible and invulnerable.
I think it's quite possible Lucifer wishes to replace TWG, I agree. I'd say the Outsiders have been trying to get in even before the Fall. Well before in fact, depending on when you think the Fall happened. Lucifer had a purpose once after all.
I like that Black Council theory, they are new. They could also just as easily be a tool of Nemesis. We'll see.
I think that assumes the body Drakul is in is the body of Vlad Dracul II of Wallachia, rather than Vlad II simply being another persona adopted by the being currently known as Drakul. The body/vessel could be from ancient times. We don't know when the "utterly inhuman being" became trapped in mortal form. We do know Drakul has been operating since the earliest days of mankind, or close to it. We also know he has held many, many personas from history (although not all famous, maybe not even most). I think he is very like Vadderung. A very powerful, elemental being that is distilled into a shape humans can more easily accept in order to deal with them. A facet of the greater being...whatever Drakul really is. It gives such beings much more leverage over destiny than they would otherwise have, at the cost of the majority of their power.
I think the Norse might have been guardians between when the Greco-Roman Gods were handling things and Winter as it currently stands.
Assuming you're right about Drakul and Lucifer wanting to be the Creator, and assuming they could usurp that role, why would Uriel try for it? What about Michael (the Archangel, and the leader of all Angels)? Or Rafael, or Gabriel? Let alone any other being?
There is an incredibly good storyline in the Lucifer comics (a very interesting read if you ever get the chance) about this very idea. The show that was based on the comics...was a very bad adaptation (however enjoyable it may be on it's own merits). I couldn't get through much of it as it was so far from the comics, and the comics are just a far better story.
Yikes, scary thought having Drakul as Leviathan. I haven't really seen a sea-type connection...but it's intriguing.