What was it we were seeing?
The WoL is travelling forward in time to return to the present. On the way back they collide with a shard. These shards seem to represent memories. If these are Venat's memories they are as incomplete as poor Elidibus's.
In which case maybe I and others have been way too hard on her. The cutscene is not literal. And if it is not an accurate portrayal of events then what parts of it are accurate and what parts are not?
Final days. Her memory matches up with Emet's version of it in his dungeon.
Did Emet and Hylthodeus meet up in the street 20ft from a guy getting eaten and Hythlodeas waved goodbye while Emet did angry guy fist clench? I don't think so. Venat was no longer part of the 14. She would not have been involved in that meeting. The goodbye is probably what she thinks happened between her friends, with the location just being jumbled up in her scrambled memories.
There is a NOTICEABLE lack of Zodiark in her memories of what happened. Like she completely blocked out the part where he saved the planet.
She mentally skips forward but shows no passage of time in her memory. (Also important to note is that throughout all this she is not involved in what happens up to this point. No attempt at saving people from monsters, etc. She is removed from what is going on. Some kind of Dissociative identity disorder. A mental disorder, characterized by multiple personality states and amnesia. I googled that to make sure I spelled it right and holy crap that definition hits Venat and Elidibus on the nose.)
So now Hydaelyn is facing down the worshippers of her enemy, Zodiark. And at this point she is bound by the purpose of her summoning. To stop Zodiark. Whatever Venat is in there cannot fight that core compulsion of why Hydaelyn was summoned. She confronts these followers and a somewhat odd conversation takes place. She then raises her sword and enacts the sundering. There is no battle with Zodiark.
That strongly contradicts Emet's version of events. His story made it seem like Hydaelyn and Zodiark had a long drawn out battle and in the end Hydaelyn won, but this caused the sundering. Who we believe is very subjective to how we feel about the characters.
Hydaelyn blocked any memories she had of her confrontation with Zodiark. IF it happened. If she never battled him and instead bypassed his greater power by sundering the world that is a possible explanation.
Venat then walks forward in time getting covered in black stuff. I do not think this is literal. This is probably not even remotely close to a memory and more like an emotional impression of what she has been going through.
Based on all this I think it is fair to say that once Venat was made into Hydaelyn she lost large parts of herself. She may have literally sacrificed huge parts of what made Venat, Venat.
For my own part going forward, I am going to cut Venat some slack. Not a perfect being but she was trying to do the right thing.