What's the point with that quite lackluster story in Endwalker?

[CrownySuccubus]

She knows what will be the result in terms of the bad things that can happen, but the result was not why she sundered mankind. That's why she pled with the Ancients. If they didn't choose to go with their plan of sacrificing the new life to return their old lives, I don't think she would commit the sundering.

No, the result is exactly why she sundered it. We are specifically told by Venat herself that the entire purpose behind the Sundering was to induce mankind to death and suffering so that they could learn to overcome it rather than deny its existence. Sacrificing the lives to return to their old lives was an example of the Ancients denying the existence of suffering.

Your examples still do not apply because they are about specific injuries. The sundering is not about specific injury as the whole world was sundered.

You're really trying to stretch the definition of "killing" if you think "specific injuries" is a requirement. But, regardless....

If what you say is true, then the planet itself is injured and dying.

Yes. You are literally correct.

Of course the sundering had to do with Zodiark. The sundering happened because she couldn't kill Zodiark, so she had to weaken him somehow, and yes, it also had to do with Meteion as an action does not have to have only one purpose.

Weakening Zodiark was a methodology to forestall the Final Days, but Venat is very clear when she sunders the world that the primary purpose was to teach mankind suffering.

Also, another factor contributing to the shortened life spans is the loss of creation magic, meaning mankind had to work harder to exist and not rely simply on creation magic. Quality of life changes alone can change life spans. That is not a direct comparison to actually stabbing an individual because the indivual was not injured. All the resulting problems happened because life is harder for them, so conflicts can arise more easily.

Dude, are you serious?

If I permanently break one of your arms, and you die because you, say, later fall from a high ledge that you ordinarily would have been able to catch and pull yourself up from if you still had both working arms, then I killed you.

I don't know what you think an "injury" is, but reducing the health, the physicality, and the ability of person to defend themselves from harm is basically what an injury is.