IMO it's completely wrong. I believe it should be absolutely obvious to anyone that Moridin and SH are separate characters, after reading the books and what the authors said on this matter. For some reason, a few people always tend to come up with those ideas that Moridin must be Taim, or that Mordin is SH in disguise, or now that Moridin & SH form a Slayer-like creature.

In my view those thoughts aren't really supported by any convincing evidence; it's rather just the ambition to come up with a "most original theory" just for the sake of such an idea.

Plot-wise I don't see any sensible reason why RJ would rather literally want a physical link between Moridin and SH (and later also Rand), instead of simply having Mordin & SH work together very closely, because they follow the same philosophy.

I believe you are simply reading too much into a few words, while you ignore the blatant rest or believe it was only stated to fool the ordinary reader, though this hardly makes sense. Thus you make the whole matter more complicated and convoluted than it actually is, likely just because you became that sold on your pretty far-fetched idea. But we will see...