The Crystal Tower raid? Oh, no no no, I have next to no recollection of those events, outside of what we're "reminded" of in the course of 6.x quests. The quotes in the first post are all taken from two sequential 6.1 quests. If anything required specific knowledge from the raid... I certainly would've glossed over it entirely, smile and nod.

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?

I'm kinda leaning more now towards Y'shtola's words being poorly chosen/translated.. Rather than directly needing some manner of guidance to a destination, the "guiding agent" may have in fact been a reference to the act of opening the gate in the first place. The gate itself is the "guiding agent" to traverse the rift. An agent, on either side, should be necessary to open a channel. While that particular voidgate remained closed for a time, the connection evidently remained, per the pact.
This would mean Y'shtola was speaking more generally, that one cannot just jump into the rift between worlds and expect to actually land anywhere.. but we don't really hear about any general "rifts" opening that aren't already connected to the Thirteenth.

It does... sorta raise an additional question of how we actually managed to open a gate on the moon... by either conclusion, there should've needed to be something on the Voidmoon to connect to.. I think they vaguely attempted to explain this away, something something Zodiark and Darkness, with a whole load of aether to punch through...

Kinda leads to the idea that voidgates are always exactly as functional as the story needs them to be at any point.

Also,