Unmarked spoilers oncoming. Basically, I'm saying here that nearly every part of Venat's role in the story is nonsensical on multiple levels.
To begin, the sundering itself. Supposedly this was done for two reasons - To increase people's ability to interact with Dynamis and thus be more capable of combating Meteion, and to destroy Ancient society because they would ultimately doom themselves. Venat's reasoning on both of these fronts is wrong. Firstly, because WoL themselves is 9/14 parts rejoined, meaning that the sundering as Hydaelyn enacted it was at least 66% pointless. There was no reason to sunder everyone so thinly when we see that even a one-half split would have been more than enough to do the job. Secondly, the destruction of the Ancients was pointless because the sundering did not inherently change the nature of mankind in the sense of always seeking out advancement and the creation of a better world. As long as humanity persists they will always seek out the best of all futures, and this is the moral motivation of all of the protagonists. As such, if mankind does not destroy itself and is not destroyed by some other force, they will eventually reach the same point as the Ancients once again, residing in a world where the vast majority of their suffering has been mitigated and they eventually lose reason to continue living. On this front Venat did not solve anything, she simply delayed the issue to some point in the future.
Moreover, doing this opened up mankind to extinction through various other means that the Ancients were not susceptible to. War and strife, disease, political manipulations, we see that countless other civilizations fell prey to such maladies and destroyed themselves. Indeed, we see that sundered life is very vulnerable to these things - In the Fifth Era the warring states nearly drained the land of aether to the point of desolation warring with each other, and it was only the setup for a rejoining on another shard which destroyed their civilizations and saved the world from being sucked dry. In the Third Era the Allagans even fall to nihility after reaching the apex of their civilization and slowly declining, at which point Xande concludes that life is meaningless and everything should return to nothing. This is exactly the mindset that Venat set out to stop from happening, but here we have a sundered lifeform reaching that same point and nearly obliterating the star in the process, and once again were it not for the setup of a Calamity intercepting things the world would have been swallowed by the Void. I'm sure people will claim that these things are wholly attributable to the Ascians, but we see time and again that their modus operandi is to hand out power and allow mankind to destroy themselves rather than directly manipulating events, and this is precisely the case in at least these two situations.
Next, we have the issue of alternative solutions which go unconsidered by either Venat or the story itself. The plot tries to excuse this in advance by introducing the closed-loop time travel and suggesting that Venat must have done everything she did purely to reach this ending rather than attempting anything else, but due to the limits of everyone's knowledge on the subject I find this to be an extremely questionable proposition. WoL knew the future as well yet chose to reveal that future to the others even after being told that it would change nothing, but Venat does the opposite and willingly withholds her knowledge despite knowing the tragedy that would befall everyone. Just on the face of it this shows that WoL and Venat are not operating with the same moral compass. But this is an aside.
Why did nobody try anything else? We're told that aether is more powerful than Dynamis despite being less abundant in the universe, so why does everybody act like Meteion cannot be confronted without the ability to manipulate Dynamis? We're shown outright that sundered life is actually more susceptible to being manipulated by Dynamis, so why is the conclusion that more aetherial density = loss? If Zodiark has the power to shield the entire planet from Meteion's influence, why could Zodiark not simply defeat Meteion without being touched by her powers? If Meteion is still an aetheric being, why did Venat not consider sundering her, as we're told that her aether is inherently so thin that she is in danger of dissipation? If interaction with Dynamis is necessary, why not create a new lifeform in the same vein as Meteion to challenge her, but without the hivemind that renders it too easily influenced by despair? Why not create an aetheric being with no soul and no emotions which is immune to the power of Dynamis? Why not create a construct that can only feel joy and infect Meteion with it? If sundered life is necessary, why not simply sunder a number of volunteers in order to confront her? Why not increase the Ancient's aetherial density even more so that they're completely shielded from having their magicks hijacked by the power of Dynamis, and confront her like that? We are not given any reason for thinking all or any of such other solutions are impossible or that they were even considered. WHY is Dynamis even supposedly necessary, when the only time we seem to use it outright against the Endsinger is with the LB3 when she calls that out as Dynamis, despite the fact that Emet-Selch, Venat, Hythlodaeus, and Elidibus can all Limit Break as well. Elidibus even has a Limit Break FOUR. This is a major contradiction.
Next, the morality that Venat displays is, frankly, terrible. She unilaterally decides that the Ancients one day coming to an end of their own volition is unacceptable, and does not allow them to even try to challenge Meteion themselves thus stealing their freedom to fight for their own fate, let alone figure out what had happened. She hides the truth of the Final Days from them, yet argues with the Convocation under false premises trying to convince them not to go forward with their plans, without telling them anything that might convince them not to. She seemingly murders a bunch of people in the street after giving a moralizing speech about burning their "wings", because they rejected her statements. She sunders the world, genocides her people, and leads all of humanity through 12,000 years of suffering without telling them why. She opposes the Ascians and the rejoinings and creates Warriors of Light to die for her cause while stopping the Calamities despite knowing that at least seven or eight of them need to happen anyway. She bodyjacks Minfilia despite being perfectly capable of talking to WoL directly, lies to WoL the person she knows comes back to the past about the past, and insists that the Ascians cannot be suffered to exist despite never having told them why their cause might be wrong. Due to knowing the future and intentionally leading people towards that future, in effect every bad thing that has ever happened is directly attributable to Venat. Even some things that were previously unexplained, like her not answering the Warriors of Darkness, allowing the First to be 90% consumed by the Light, and sending Ardbert to wander around in isolation for 100 years, can now be understood as actions she took to match up with the future she knew.
And with all of this, her motivations are completely backwards. She tells us herself when WoL reveals that she was planning to evacuate the planet that she would never do that, and instead choose to fight to the last to avert it. But that's not what she does, instead she does nothing to avert it the first time and puts all the burden of fighting it the second time on generations that will be born 12,000 years in the future. She creates millennia of suffering ultimately for the sake of one person, WoL, on blind faith that they will solve all the world's problems in their future that is, as far as she knows, doomed. And this segues in to the even worse issue with Venat.
The writing. My God, the writing. As I've outlined above, there are numerous logical inconsistencies with Venat and issues relating to the sundering/Dynamis in a lot of regards. Some other major offenders include the LB problem I pointed out above, the problem of the non-tempering nature of Ancient creations which retroactively confuses elements in Shadowbringers where the opposite was directly stated (which was seemingly invented purely to dodge the idea of Hydaelyn tempering people), and the problem of Ancient concepts not having souls, which was explicitly shocking to everybody in the short story when it happened. And of course, a side issue is that the player and the main cast hardly even has the opportunity to take issue or disagree with Venat on much of anythig. But, by far, the worst offender of all is the massive gaping plot hole that is the combination of Shadowbringers Rift time travel, and Elpis "closed loop" time travel.
Let me lay this out for you: WoL travels back in time to Elpis, and among everything else, inadvertently gives Venat the idea to sunder the world to begin with. It is WoL's presence here that motivates her to do this, because she perceives flaws in the Ancient society and their supposed eventual fate, while also gaining hope for another future to guide mankind down, eventually leading to WoL. WoL traveled back in time here and has reached this point to begin with due to the events of Shadowbringers, and the arrival of the Crystal Tower in the First from another timeline. Now in that timeline, WoL died in the Eighth Umbral Calamity, leading to a devastated world languishing in ruin, which motivates the AU Ironworks to attempt to go back in time and undo their doomed future and revive their hero. However in this timeline WoL is dead - Meaning that WoL cannot go back to the past to Elpis using a Crystal Tower on the now-rejoined-First, and cannot motivate Venat to do the sundering, thus the entire 8th Umbral Calamity timeline cannot exist. And if the 8th Umbral timeline cannot exist, that means that the main timeline cannot exist, as it is dependent on events in that timeline occurring. It's a massive two-way paradox that utterly destroys the logic and plot of the story. And this is all to say nothing of the fact that that timeline is now supposedly doomed despite a short-story being written specifically to inject some hope back into it.
All of this, I'm pretty sure, because the writers insisted on not having Venat mindwiped as well, because they wanted to tie WoL directly to her character for the sake of trying to form a bond between the two. This is a massive fumbling of the story that, frankly, I would not have previously thought the XIV writing team capable of - Simply put it is probably the single worst piece of writing in the entire game, due to how far-reaching and complete it's impact is. It's practically a case study in why writers should never mix-and-match different types of time-travel storytelling, much less in a hackneyed way that involves the necessary addition of amnesia from the outset.
Altogether, this is why I cannot consider Venat or her role in Endwalker anywhere close to a good addition to the story. She's bad on every single level, from the logical to the motivational to the basic barebones plot conception of her narrative. It's all atrocious.