The fact that apparently you aren't, saddens me in some strange way to be honest. I guess you could call it a deep respect for how a value your opinion on 'all-things-WoT'.
Even though your opinion puts a huge dent in my confidence, I still think I'm on the right track. So at the risk of making an ass out of myself... here goes;

First, let me adres the title of your post:
Well. Wierd as this may sound, I tend to agree with that. And the reason is very simple. I don't think I'd dare call Slayer an 'individual' either. And since I'm advocating that the Nae'Blis is a '24/7-creature' bound together by a Slayer-like connection as between Isam & Luc, I don't think you'd have to consider that creature to be 'an individual'.

As I posted yesterday in this topic;
Like Slayer "both are".

The main differences with Slayer are that the one that 'did live' has a mind that can channel (Ishamael) and the one that 'did die' actually 'never was born' (A Fade/ Neverborn).
So you see, "both are", but never-ever "at the same Time".

Luc and Isam both seem to consider themselves as individuals in their PoV's (WH - Out of Thin Air). One decides to become the other one when it seems more appropriate. One likes killing wolves more then the other.
So my question to you is; do you consider Slayer to be an individual? Or do you consider Slayer to be two individuals meshed together that share eachothers memories? (2 bodies, 2 minds, 1 soul, for instance)

Because if it's the latter, I hardly see your point as this being a reason for denying the possibility of Moridin & Shaidar Haran being one 'creature 24/7' (as RJ put it)
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Now the rest of your post:
As wierd as this feels for me writing this about something you posted, but that's just plain wrong.
You have no proof that Moridin was in that room, prior to him commanding Moghedien to open her eyes. Stating as fact Moridin was already in the room the moment Shaidar Haran was transporting Moghedien there is jumping to conclusions.

And like I asked Etzel earlier, this begs the question as to why Moghedien had to close her eyes and was told to keep them shut until she 'was commanded to open them'. What was it that Moghedien wasn't supposed to see those few seconds? And why -if they were seperate beings- did Moridin and Shaidar Haran have to agree on having her close her eyes? (Shaidar ordered her to shut her eyes and Moridin told her 'she could open them now', thus full-well knowing Moghedien was ordered to close her eyes)

The questions you should really be asking yourself are these;
1- What exactly had to remain unseen those few seconds by a spineless, selfish woman who was -literally and utterly- being owned by Moridin?
(How about the transition from Shaidar Haran to Moridin. )

2- Why wasn't Shaidar Haran in that room too, if they are seperate beings?


Like I said when discussing the title of your post, we agree here. I'm just adding the "Slayer"-bit to the equation, making the point you raise moot (IMO).
Personally, I think this hidden connection is the main reason for Slayers whole existence in the story! What and who Slayer is, is slowly fed to us from book 2. Book by book we learn more about how Slayer works. And at the grand finale of this series RJ is going to slam down his ace-up-the-sleeve on the table. RJ needed a way to make his revelation of what the Nae'Blis truly is, feel 'intuitively obvious'.
He did this by adding the Slayer-character.


Again; agreed! But again, the mechanics of how Slayer works actually helps this.
Because to be able to channel, you need a living mind. (per Moiraines words to Egwene back in TEotW). RJ's own words tell us that you need to be able to channel in the first place to be able to channel the True Power.
It's safe to say that Shai'tan doesn't have a living mind. Far from it in fact.

I think all Myrddraal have always been closely linked to Shai'tan, regardless of the degree of freedom of Shai'tan. They are literally half man. The other half is nothingness (and there is only one Master there).
I think all Myrddraal could have channeled -had they been humans-. It is what triggers the change from Trolloc to Fade. As we know, TP and OP don't mix (see taint on saidin for instance). What if the connections that Aginor made with the TP in the Trollocs design 'snap', because the OP runs through the system and only the part that is human forms the Myrddraal. The rest is void. The terrain of Shai'tan.

None of the Myrddraal can channel though (even though they have the potential, Soul-wise), because a Neverborn lacks one vital piece to be able to channel; a living mind.
After all, we could hardly call a Neverborn a 'living being', now could we? (this is an understatement, I know)

I think linking a living mind to a Fade solves the problem of a Fade not being able to channel (the so-called True Power).


Totally agree on all points. There's one thing I'd like to add though. I view 'cause and effect' differently then you do.
I think the reason why Shai'tan was able to be present in Shaidar Haran the way he is, is due to the link to Ishamaels heavily corrupted mind. So it's not a matter of Shai'tan "willing it", but more the fact that the posiibility arose.

I also think that it's this link that allows Shai'tan to be more present on this side of Creation and that that fact makes the DH harder to kill.

I disagree fundamentally here. The way I see it, Shai'tan represents the absence of everyhting (and then some). He is the Void. Nothingness. Uncreation. Zilch..Nada.. you get the point.

Shai'tan can't "invest massively more into a single Myrddraal", because I think there'd literally not be enough left of Creation to invest in!
Shai'tan already walks a very thin line with Myrddraal as they normally are!
They already stand partly (probably half-way, being half-men as cast from the same mold) outside creation/ time as is. Any more, and there just isn't enough of Creation left to be able to function inside Creation. Maybe that's why some of the Myrddraal die at..ermm.. 'birth'.

100%. Yet this doesn't disprove Shaidar Haran & Moridin being linked in a Slayer-like fashion at all. In fact, I'd say it supports it.

We do know about that connection. In fact; we're discussing it right here!
Working together apart! That's classic (and very illogical and wrong I might add) If it's ONE thing we know for certain if it concerns Shai'tan, then it's the fact he doesn't share/ trust ONE bit. It's completely anathema for Him! What were the words? Uber-control-freak. Working together?
I'd never thought I'd see you write those words if it involved Shai'tan to be honest.
Shai'tan doesn't trust/ work together. He rules and grabs what he can where he can! Nae'blis? That's Shai'tan himself for as much as he can shove into Creation!

Again, you say something like it's fact, while it isn't! We see the Watcher spot Sammael doing something dubious. I know the on-line world thinks that they saw Moridin. But there's just as much to say that it was a certain Fade with what's left of Ishamaels mind.
Care to explain how "Moridin" saw the link between Sammael & Grandeal 'dissolve', while both Sammael and Grandeal still held on to the Source?
Or care to explain how the Whatcher 'ghosted through the trees soundlesly' while following two channelers with heigtened senses?

You say Moridin watched Sammael. I say it was Shaidar Haran.
Makes way more sense too in more ways then one.
The "Watcher" is a Lurk(er).

You think Rand would have accepted the hand of a Myrddraal then?
"Hello, I'm the "Hand of the Shadow" and I've come to save you, because to many well-laid plans/ traps have to be re-set when you die.."

Well. I'm looking forward to your reply.
Cheers,
Mik