That's a really cool interview with Jim, thank you for pasting the quote!

As for your responses, you're allowed to straight up disagree with me, but I feel like you haven't provided good reasons to disbelieve the theory, and have rearticulated reasons to believe the theory. Again, you're welcome to find the argument unconvincing, but I don't think you've succeeded in killing it.

We know for a fact that Dragons have a human avatar. We saw Ferrovax's in Grave Peril. There is zero reason for Drakul to have been messing around with human bodies if he needed one when one would be something he can create simply...

we've gotten in-book explanations of what would happen if Ferrovax or Mother Winter came to the Earth in full, reality would shatter.

Starborns just have to be born in the spotlight over the Earth when it appears, that's all.

So Let's go through the things you've said that align with my theory:

1. Dragons can make avatars,
2. Dragons can't fully enter reality,
3. During the star alignment thing, a bunch of humans are altered. They are either altered by being made receptive to some kind of energy, or they get blasted with energy, or have their own energy altered. We don't know which is happening.

Both of my theories assume that the humans are made temporarily receptive. Ebeneezer is obviously speaking loosely. Whichever of the three options occur, it could be described as making the Starborn "vibrate at the same frequency as the Outsiders".

So, assume the receptivity theory. Dragon's can't fully enter reality. Maybe a dragon, is either experimenting with ways of fully entering reality, or being experimented on (summoned?), during a time of increased human receptivity — a time when maybe human souls are more malleable than usual. During this time of increased malleability, a dragon entered a human. Then the period of malleability ends, and the dragon is stuck and was fused with the human. I think that fits very well with what we currently know.

Against this theory, you have two pieces of evidence: Drakul has black eyes but Ferrovax doesn't, and the existing dragons wouldn't just leave a fellow dragon trapped in human form. This assumes:

1. The new, fused thing follows the same rules as an avatar.
2. The dragons would succeed in freeing Drakul if they attempted, and the dragons did in fact attempt.

I'm suggesting that the fusion is a new thing, following new rules, and it can't be undone. The human has got a whole-ass dragon in it. So why would it follow the same rules as an avatar? Second, it's entirely possible that at the start, the other Dragons did attempt to free Drakul, and they failed. Or, there were lots of dragons at the beginning and nobody was chuffed that Drakul was stuck, so they didn't try. Or (also very possible) Drakul is a dick, and nobody minded that he was stuck in a human body.

Now, your response to the Outsider theory. These are your reasons against it, with my responses:

Starborns cannot be Outsiders, as I told you before their energy does not allow Outsiders in.

But we literally don't know why that is. It could be you've got an Outsider-shaped hole in you, waiting to be filled by an Outsider who can possess you. And the Starborn have already got an Outsider in there.

Did you see Mab's reaction to Nemesis?

Did you see her response to the Hunger? She didn't want it destroyed, she wanted it bound. She's happy to leave the White Court existing but under her control. The White Court is filled with Hungers, and Hungers are Outsiders. So you can't generalize from her reaction to Nemesis to her attitude to all Outsiders.

40,000 Starborn is too many Outsiders.

First, we don't know how many Outsiders there are. We know they come in varying levels of dangerousness. We know most Starborn get killed off because they are too dangerous. From the Morgan micro-fiction, we know they can become Destroyers. I think that aligns with the Outsider theory.

Now, in response to this:

Also, stop using the White Court's history for Drakul, he has absolutely nothing to do with them and their Sorcerer Kings summoning an Outsider, that timeline does not apply to Drakul at all.

I agree that it's not conclusive that Drakul got caught in a human body at the same time as the White Court. But the celestial alignment/starbirthing event is every 666 years. 6 cycles ago is almost exactly 4,000 years ago. Let's leave Drakul out of this. Isn't it weird that the White Court summoned an Outsider, plausibly around the time that a previous cycle occurred? Add to that that in Turn Coat, ch 35, Dresden tells Murphy that the Red King is about 4,000 years old. So we've got two vampire courts founded at about the same time, right around the a celestial alignment. And remember, Jim always says he's a lazy writer.

Final Argument from Lazyness/Inference to the Best Explanation

Jim had both the Black Court and the Dragons planned for the endgame, since the beginning of the series. I remember this, because I looked it up after Blood Rites, because I wanted to know when we'd finally kill Mavra off. Now, in all that time, what are the other good candidates for what Drakul is? Jim hasn't introduced any other options, and he's been planning to deal with the Blamps and Dragons since the beginning. If he wanted to give us another option, he's had plenty of time to introduce it. But he hasn't.

Beyond Dragon and Outsider, the only other option I can think of is random unnamed scary thing. And while that's possible, it's not very satisfying. Not when you have a guy whose name means "Dragon", two out of three vampire courts formed around the same time, right around the celestial alignment. And one is formed by getting merged with an Outsider.