You suggest that Moridin and SH are one creature, fused together like Luc and Isam are, but actually also Ishy and SH 0.5. were already one creature. Your evidence is that the Trollocs named Ishy Ba'alzamon, and consequently he must have a physical link to a Myrddraal. The other evidence is that the Nae'blis is just half a step below the DO, and consequently the DO would fuse himself together with his Nae'blis. Finally, Carrdin was visited by SH 0.5. but after Ishy's death, Carridin was left alone for some reason, which is obviously that Ishy and SH 0.5. were one creature.

Irrespective if this evidence is in any way convincing, or if it couldn't be explained in more reasonable ways (namely that Moridin and SH are simply closely working together and not physically linked), you have to note that if we read Moridin's or SH's PoV neither indicates at all that both are one being (if we read Isam's/Luc's it's immediately made clear that they are fused together). In the same way, the authors always distinguish between SH and Moridin in their statements. Why do you think, they would fool us that way, just for a lame twist?