The idea that Venat—characterized fundamentally by her unending love for the world and all its creatures—was not motivated by her desire to save the new life that had been created by the second sacrifice, and more generally all life in the universe, is absolutely nonsensical. She was literally the woman who created the faction who argued against the sacrifices and continued to argue against continued reliance upon Zodiark to reproduce what had been lost instead of moving forward and accepting the suffering they had gone through. You say that her whole thing was a purely utilitarian plan to ensure that life could manipulate dynamis, but that's not a motivation, that's an goal.

Why would Venat want life after the Sundering to be capable of manipulating dynamis? Why would she ensure that she could always find Meteion no matter where she hid? Why would she set up events so that the people of the sundered world had a chance at defeating the being that wanted to end all life in the universe forever?

The answer is, very obviously, that she cares about life in general and wants it to continue existing. Based on the information she had and the concerns she had about what could be shared and who she could share it with, she made her choices to attempt to stop the Final Days, and was not successful. Then she attempted to convince the remnants of her people to avoid sacrificing the new life they had created to repopulate the star, and she was similarly unsuccessful. Finally, she went through with the Sundering, and in doing so created people who were able to manipulate dynamis and would have a chance at defeating Meteion—because Meteion wants to kill everything, and Venat doesn't want everything to die.

I understand that people's opinions aren't going to change, and that getting anyone who came out of Endwalker loathing Venat and her writing to think differently is a pointless exercise, but the absolute least that should be done in an argument is to be accurate about what is being argued. Yes, Venat confirms that part of the rationale behind the Sundering taking the form it did was to create beings that could manipulate dynamis, but unless you think Venat just did that for fun the obvious second part of that sentence is "So those beings would be able to defeat Meteion and stop her from ending all life in the universe", something Venat would only care about if...she cared about life in general.