Even then... what, do people think Venat's intrinsic character is 'let's shatter the world when it looks too good'? That this was the end goal of all her lives, she just happened to pick the Sundering as her avenue that one time? Reincarnation
was a standard part of how the world worked even before the Sundering, wouldn't a soul with a predeliction towards planet-cracking have feasibly, y'know, caused some severe problems before then?
It's hard to get a bead on the 'intrinsic character' of Venat, since we don't have a lot of time with her when she's putting on a genuine face, but I would probably characterize her as 'unyieldingly principled'. With the Sundering, she made the ultimate statement of the Ancients' actual principles, when even most of the Ancients went against them. And even after twelve thousand years of walking the hardest possible road in every possible way (especially emotionally), and never once wavered. And this isn't emotional deadness, or psychopathy or anything someone might want to negatively ascribe to her; she is empathetic to the highest degree, and still goes on.
...which means that, ironically, the Goddess of Light was the greatest Dark Knight we've ever met, as she more than anyone is
of Unyielding Principle. She's not someone who chooses violence for fun or for ease, she's someone who will do what's right, no matter what. That's the intrinsic character she would bring, not 'mass destruction because you've got it too good'.