6.1 plothole?

[Cleretic]

However, if I may make some assumptions here: the "guiding agent" serving to draw us through would have been the Cloud of Darkness. Or maybe Doga and Unei?

Yeah, the CoD of Darkness was my guess for that. If the 'guiding agent' is specifically sort of a beacon to aim for, it makes sense that she was ours: 'aim at the biggest ugly we can find'. It actually explains why exploratory projects like this hadn't happened before: if the hard part is finding a beacon to aim at in the first place, a mundane exploration is actually pretty difficult, because you need an exceptionally non-mundane target to aim for. (Not to mention the horrors.)

But if that's how it worked for us... then that's how it worked for Azdaja, surely. All factors were still the same then, so she could've easily just gone 'let me at it' and beelined. As for us managing the moon transit, that's actually very similar: not only was there Azdaja to aim at, and not only was there a Golbez nearby to aim at somewhere... but there was also a big stagnant morass of Zodiark aether lingering, too. All of those are pretty easy bullseyes in this scenario.

I still think that on a general storytelling perspective, the idea with travel to the Thirteenth is that the 'tunnel' is the easy part: digging the entrance/exit, and figuring out what to do when you get there, those are the hard parts. But actually getting there? So easy a child could do it, and voidsent child-equivalents frequently do, which is specifically thanks to the fact that the Thirteenth is just (meta-)physically closer to the Source. If travelling to the First is a cross-country trip, traveling to the Thirteenth is driving to the shop around the corner; it's still possible to crash, but there's not that many ways to screw it up.

[Hasrat]

But if that's how it worked for us... then that's how it worked for Azdaja, surely. All factors were still the same then, so she could've easily just gone 'let me at it' and beelined. As for us managing the moon transit, that's actually very similar: not only was there Azdaja to aim at, and not only was there a Golbez nearby to aim at somewhere... but there was also a big stagnant morass of Zodiark aether lingering, too. All of those are pretty easy bullseyes in this scenario.

Yeah, as I wrote it out, it made a sort of sense. I think it may have just been explained/interpreted poorly in game in that moment. The "guiding agent" comment referring more to, essentially.. "you can go knocking on the door, but someone on the other side needs to open it, else you'll be lost at the threshold of the between."
CoD had already opened the door on their side, as Allag had opened on ours.
As for the moon... well, I guess we'll just chalk that up to using a battering ram to knock on the door.

As for fissures.. I suppose in this context, Varshahn's comments could instead be taken to mean natural fissures do not need someone here to "open the door," they're just climbing through an already open window, or a doggy door, or our chimney, etc.