The word "failures" could really mean anything there, but even assuming that was what they meant, it doesn't make it any less silly. The Flood of Light in particular is a tragedy she could have very easily prevented by giving slightly different guidance. And if she was trying to change the future, why not behave in ways contrary to what we'd already told her? She knows that she's going to found an organization opposed to Zodiark to summon Hydaelyn after the Convocation refuses to back down from the sacrifice plan, and how this all ends in tragedy, but plays into it directly, point by point. That's not how someone trying to change the future would act.
Like, I'm not saying you can't be charitable towards the script, and use incidental dialogue like you're doing to interpret it in a way where her actions as a character loosely make sense one way or another. But it's obviously a little ambiguous - the people defending the clarity of her motive in this thread don't even seem to have the same interpretation among themselves, with some arguing she was trying to change the future and some not. I think the writers were probably "subtle" about this stuff because they realized that the scenario they'd crafted for her in Endwalker (which we know was a bit of a troubled project compared to earlier expansions because of covid and so on) didn't quite fit with the stuff they'd already established. So they kept a lot of points vague in the hopes that people wouldn't worry about it and just go along with the general themes.
So instead of a clearly written and objective Venat, we end up with a sorta build-your-own-Venat kit, where everyone can focus on different suggestive moments and lines to create their own motivation for her. The result is that most people like her, but barely anyone has the same interpretation of what was actually going through her head when she did the stuff she did.