I agree in part, but I’m always wary of ascribing too much to the supernatural when there’s a mundane reason that would cover it (which is a theme that is repeated often in this series and is why Siobhan has become the Raven Queen - though the argument can be made that she’s often dense to the opposite situation).
Yes, he feels like a different person to Edgar and to his previous iteration(s?). He’s also gone through massive trauma and literal life changing events. These things can have a massive effect on people and make them reevaluate their lives and themselves. Add to this that he’s not fully sane and (I suspect) his brain is not working in entirely normal ways anymore. He likely has extra senses on top of everything which is fairly mind bending in its own way. Some part of him with similar thought patterns has been writing in his journal thoughts he has no memory of having. I wouldn’t call it a split personality but a splintered mind where the shards have the same personality. Although maybe not all of them.
One thing is incongruous to me - he no longer hates and fears those different to him, but when he became agitated in the mental hospital he spoke of “that water bitch” and his way of speaking became meaner, more fearful, more suspicious, more like the original Edgar.
We don’t always know our own minds, and I would imagine that’s especially true when you have parts of your psyche that are completely divorced from each other.
When this happened to Siobhan she spent days piecing her mind back together and repairing the damage. She hasn’t been losing time since.
I’d be very interested to see what happens if she spends time trying to use the same technique on the Archaeologist.
There are definitely similarities between the cases, but I’d argue there are still massive differences as well. To me, the biggest is that the Archaeologist still feels human and has human concerns. He feels like a shattered, mentally unstable human, but a human nonetheless. The aberrant the was once Claudio did not feel human. He was distinctly alien, mimicking human behaviours. He did it well enough to fool others, but he was in full command of himself.
I pause here to reflect on Moonsable, who was possibly an incomplete aberrant. She broke using very minor magic and wanted to be beautiful, so her aberrant reflected that desire, taken to the extreme. But in the light she became a broken, twisted and pained human once more, although her mind was much less coherent than you’d expect. I would say that that is evidence of the aberrant state being less well understood and less binary.
The Archaeologist has no anomalous effect. As far as I can tell he hasn’t even attempted to cast anything, though I’d be intrigued to find out how he got out of the asylum without doing so. He thinks of ancient knowledge, yes. But he’s not like a junky craving his next hit of magic, which makes me think he hasn’t cast through his flesh.
My parting thought is this: the Brillig are widely thought to have created the Black Wastes. The Brillig were capable of multicasting. Siobhan, with her fractured but whole mind is capable of the same. The Archaeologist, who has gone into the Black Wastes, has a fractured mind that is disjointed and his magical capability is unknown.
I am hoping for a Christmas chapter from Azalea tonight 
it would be the best.
Would it put any of this speculation to rest? Probably not, knowing her love of cliffs! Am I craving my next hit of Siobhan’s story, anyway? You better believe it.