Late to the party, but the sacrifices were not a factor for Venat, in fact, she consumed the souls of her own followers to become Hydaelyn which is more than what Zodiark did. According to the LL Q&A, her motivations were a combination of believing the Ancients would always be their own downfall and believing them incapable of defeating Meteion without the ability to manipulate dynamis. The problem is that, much like Hermes, these were solvable problems had she bothered to discuss her concerns. Instead, she formed a rebellion, lead a coup, usurped Zodiark as the 'will of the star', and perpetrated a cultural genocide so none but those who escaped the sundering could oppose her.
Additionally, this was all done with no guarantee of success as by the time the she meets the WoL we have no idea what we're up against or how to stop it, so her choice becomes a gamble of astronomical proportions (not to mention putting Etheirys at risk of other world ending fates). The argument that she must maintain the time loop not only removes all agency of her character, but of everyone else as well. You can't excuse Venat for 'playing the part' and still claim that everyone else had free will. Going back to one of Ardbert's iconic lines, "We did everything right, everything that was asked of us, and still—still it came to this!" Exactly. Given that Venat knew how the unsundered would react to the sundering also makes her an accomplice to every rejoining. The fact that we have no evidence she was willing or able to assist the shards, including her backup plan being to abandon them entirely, is also particularly damning and makes them seem to be little more than collateral damage to her goal.
Given all these factors, the single only time you can express anything negative to Venat is on the boat where you can say you can't trust her. This is long before Elpis. Even then, you have Krile so enchanted by Hydaelyn she offers up her body to her while we're still supposed to be in skepticism mode knowing she's a primal but not what her intentions are. There is also a noticeable shift in everything that is a result of the sundering being attributed to the Final Days and everything that is a result of Zodiark being attributed to Hydaelyn. Y'shtola even says in Thavnair (after the moon so the Scions knew better) that Hydaelyn forestalled the Final Days by sundering Zodiark, none of which is true. What I found particularly shocking is the sundering made people exponentially more susceptible to the Song of Oblivion not only in terms of chain reactions forming, but in the destruction of souls. It's ironic that there's so much debate surrounding the unmaking of soulless creations in Elpis, but Venat is consistently shown to have no care when it comes to people's souls.
Contrast this with Emet, who you are only ever able to address as a hostile entity throughout 5.0. He is also routinely condemned by the Scions regardless of whether or not they sympathize with his motivations. As examples, Y'shtola calls him out for murdering millions and Alphinaud says (see image), but conveniently no one has a negative word for Venat about anything she's done, on the contrary, her choices are defended and excused while the WoL's dialog options towards her are wholly positive. This also reflects poorly on the Scions because it makes them appear hypocritical and self-serving. There's a reason why many felt EW was the epitome of "rules for thee, but not for me".
This next part is subjective, but I did not find anything sympathetic or relatable about Venat. Emet wanting to right the wrong of the sundering was understandable. Venat having potentially life saving information and withholding it was abhorrent to me. Her deciding on behalf of all of Etheirys that she knew best based on unfounded beliefs and flawed logic I found unconscionable. Quoting Brinne: "The fury of one friend in particular over the montage sequence was based around how it was contorting itself to uplift the struggles of Venat as a tragic individual, asking us to focus on her perspective and how much the Sundering was hurting her, and used everyone she had killed and subjected to suffering as narrative accessories for her noble torment." I felt the same and found it repugnant.
When people say they don't understand why someone would hate Venat, I likewise can't understand why anyone would like her. As far as I'm concerned, she is one of the two primary antagonists in the history of the world's lore next to Hermes. The people of Etheirys, both unsundered and sundered, were her victims in a multitude of ways. I'm also baffled why anyone when faced with the person who ended their original existence would be trusting because this time she's on your side. It ignores that Venat had no loyalty to anyone or anything but her ideals and would've acted against the WoL & Scions if it would have furthered her goal.