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

[Brinne]

Venat specifically mentions the sharks as being made because it became trendy, not because of the world actually needing them. Others are actively making the world a better place and creating things that actively fit in the world as a whole like it was intended. Others like one Ancient in a FATE sends us against a bunch of strong creations because he thinks we're a disposable familiar that happens to be strong and he wants to make something strong with no other purpose given. The only reason why you would need to create monsters to fill your ecosystem is because you've created monsters already and it becomes a sort of arms race in order to keep everything balanced. Elpis is also dangerous enough where it's been mentioned that Ancients have been injured or killed so it's not all sunshine and roses and then Pandaemonium, which is a league of its own.

That was Hythlodaeus, not Venat, for what it's worth!

Ecosystems are complicated, and again, the purpose of Elpis is to thoroughly test to see how a creation could fit into and contribute to an ecosystem. The Ancients are human, and therefore get excited about trendy stuff the way we modern humans get excited about trendy clothes or trendy food, and thus go on killing and/or colonizing sprees. This doesn't make them bad, it makes them people - and their society as a whole is responsible enough to recognize that and thus have a process to make sure as little harm as possible is done. Not to mention, even if you WANT to criticize the Ancients for stuff like that FATE series or the creation of Behemoth, that's immediately undermined because the Warrior of Light is happy to participate and help the Ancients in that process. "Hm, okay, I'll give this guy feedback about his predator creation to end up with a Meteor-slinging Behemoth. Also this guy is bad and wrong for making Behemoth (which I actively helped him with)."

Also, what you mentioned about "it's established that people are hurt and killed in Elpis" is yet another funny thing, because the story simultaneously tries to argue that the Ancients were selfish and spoiled because they didn't deal with hardship or being hurt. Except when they did. Ancients Are Wrong No Matter What continues to be the fundamental baseline.

Hell, not to mention, shouldn't we be cheering on the Ancients, given Endwalker's purported values, for creating a cycle of work that continues to necessitate other work? We don't want them to actually reach a state of a perfected, balanced ecosystem, become stagnant, and lose purpose, right? Wait, no, but that's bad too, wait--

The scariest thing about the Ancients overall that we learn later on in that whole arc isn't that they make this stuff, it's that they individually feel like they have the power and the right to make decisions for the whole planet and they they know best and that's how you get people like Hermes, Venat, and Emet-Selch.

Three individuals were like this - two of which are singled out for being extremely weird Ancients who felt dissonant from the values of most other Ancients, and the third who underwent an insane level of trauma that would be incomprehensible for basically any of us. Extrapolating three individuals all noted to be very unusual, or going through extreme circumstances, as reflecting an entire race of people immediately becomes problematic and ridiculous, especially because we see it demonstrated and repeated that as far as overt cultural values, trying to avoid arrogance and hubris is something they actually prioritize. And this is yet another thing that honestly just makes me go "man, wish we had what they have." Imagine if our humanity actually felt a similar sense of responsibility to collectively work for the good of mankind and for the planet as a whole. I might not be melting in this horrible summer heat and whining constantly at anyone who will listen about how The Sun Was A Mistake.