[LVL 87 MSQ SPOILERS] I’m so confused about that cutscene

[Illmaeran]

The whole thing is a montage. She wasn't literally calming walking down the street while things were killing and eating people.

I do agree it's doesn't show the passage of time very well in the initial parts, though.

I have a different take on it. While I agree the initial scene being something of a montage, it seemed more to me to be using her calmness as a foil for the chaos going on in order to emphasize the horror of the event. It could also underscore her fore-knowledge of the event, its inevitability, and the necessity of it to protect the future.

The parting of Emet-Selch and Hythlodaeus seems to me to symbolize the gathering of people to summon Zodiark. The looks on their faces were those of friends taking action, knowing they would never see each other again. Not being an uber-lorehound I don't know if the world continued burning for a time after Zodiark was summoned or if it stopped immediately. My understanding of the situation was they summoned Zodiark, who then stabilized the world, and the second sacrifice was done to return the world to its original state, which Venat/Hydaelyn interrupted.

The scene of her walking, to me, portrays the passage of time and her waiting for the WoL to be born while experiencing the various Joinings. After spending so much time getting us used to seeing Venat, using that form was more impactful to me than simply seeing a big crystal floating through empty space. I had associated Venat's form with Hydaelyn's "residual self image" to use Matrix terminology so having a face and body to express continued pain and effort was relatable.

[Arzalis]

The parting of Emet-Selch and Hythlodaeus seems to me to symbolize the gathering of people to summon Zodiark. The looks on their faces were those of friends taking action, knowing they would never see each other again.

Hythlodaeus was one of the people who sacrificed themselves to Zodiark. We talked to him on the moon during the part where we saw all the souls Zodiark had kept from the initial summoning. Their conversation was him telling Emet he was going to do this and Emet being unhappy/upset about it. Also really contextualizes why Emet wanted to bring everyone back. It wasn't nameless people to us now, it was someone we have interacted with. It helps that Hythlodaeus was a really likeable character, imo.