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

[Lauront]

The Ancients are a lot like the Occuria. They have processes to decide what is "worthy" to live,

No, the star decides that by deciding what to bestow a soul upon or not. What they work on is arcane entities/creations, no different to sprites, egis etc., which may gain a soul if the star deems them suitable, at which point they become animals etc. And their criteria for whether a creation gets released to the star are based on how well suited it is to a number of criteria fostering the star's own biodiversity, how well it integrates into its ecosystems etc. We have to remember that creation magicks come as naturally to the ancients as breathing, so in many ways it is admirable that they focus them in this productive a way. They even saw the coursing of their own souls through the star upon death as its lifeblood.

which was one of the main things Hermes took issue with.

He could not even bring himself to accept the death of a blatantly deadly species like the Lykaones, which would decimate other species; and at that point these things are still presumably arcane creations, not that it matters hugely. He could not understand why his mentor would eventually want to return to the star. He did not find an answer that satisfied him in any star, while designing Meteion really poorly to deal with the grief she'd encounter and then selfishly refuses to prevent her from falling into deeper corruption. His fellow researchers were endlessly accommodative towards him, even deviating from their usual process of adjusting the concept for efficiency's sake (it should be noted from the sidequests Hermes is not alone in entertaining such ideas, nor is he alone in grieving creations prematurely ended.) The easier answer here is that the guy is a nutjob, who ultimately cared so much about life he doomed nearly every single star in Meteion's path to death, all because he wanted to vindictively frame a question while hiding all knowledge of it to make it "fair", a cruel streak which survives in Amon who himself is dissatisfied with any answer he receives. So let's not pretend he's some wellspring of empathy.

They've set themselves up as the arbiters of what happens on the star. Except for a couple of exceptions, they won't intervene to help others. There's that one pair in Amaurot who are arguing about just that.

Ya, it's called a debate. The ancients liked having those. The premise was whether they'd deprive that other city state in question of its autonomy. It wasn't out of some desire not to help it, but whether it would be suitable to do so. In the end, they were actively researching the Final Days for the sake of the entire star. They did not universally butt in to other cities' affairs but stating that they did not intervene to help others as a rule is a lie.

They hold themselves aloof and disconnected and have one seat on their Convocation that does their dirty work in going out and understanding civilizations for them.

They all originate from said "civilisations". The chair exists for the very reason that the Convocation wanted to understand what is going on in the broader star to orient its decisions, so that is a bizarre claim. Hades himself had a background as someone who travelled a lot. It's not that the other seat occupants did not necessarily travel, but that that seat (Azem) was dedicated to it for the purpose of providing them information. The other seats all had their own spheres of expertise and responsibilities, like any real government. You're inventing a caricature. These are the sort of feelings animating the Convocation:

And they consider that person the weirdo. The right or wrong of Venat's actions in XIV can be debated until the cows come home, but she did put the control back in mankind's hands, for better or worse.

Hmmm no she didn't. Mankind was the ancients, represented by the Convocation as their governing body, so you're setting up a false dichotomy from the outset. Reasons for it aside, she sundered her own people and every other life form on the star when she didn't like the answer to her platitudes which failed to explain the situation, causing a huge civilisational reset and degradation of life, and she does not even accept the core premise behind Hermes's challenge, so much as try to answer the test he set. The sundered are not exactly more empathetic to lesser life forms, be they created by their own hand (arcane entities etc) or not (animals etc); if anything, the opposite. As to Venat's character? She's considered eccentric, yes, as is her successor. What of it?

Meanwhile, the supreme deity set mankind the test of either her champion besting her or if they failed, taking their leave of the star.