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

[Vyrerus]

I don't believe it's discussed enough how Venat/Hydaelyn has no downsides

Well, she does have downsides. They only get passing mentions. Which are either forgotten or ignored.

The biggest downside is that in order to even give her the Hydaelyn powers, she had to sacrifice all of her followers to herself, souls and all. They should have names, and they should be talked about, but they aren't.

She doesn't decay of the mind as much as the Ascians, because she didn't have to live in the real world. She had her follower's lives sustain her form after all, and she never once left her primal form like Elidibus.

And it's just my opinion, as the game's cast sure don't make any commentary on it, but Hydaelyn droning on still about Light = Good, Dark = Bad after everything we've been through seems to me like a crack in her mind. She sounds like a zealot, but of course, she is her own biggest fan anyway.

It's less about tropes or being cliche and more about suddenly making the character who supports us and saves our life on multiple occasions over 10 years into a villain just because people caught the feels for the Ascians isn't great writing. Considering Venat was in 3rd place in popularity polls in Japan, I don't think she's the universally panned figure you think she is.

Ultimately the game isn't about the Ancients.

They already started walking towards that path in Shadowbringers when Emet-selch revealed the truth of the world to us. They further committed to that path with the dialogue option choice on the boat at the very start of EW. They hammered in that Venat was a villain when she chose to Sunder the world rather than find a better way. Specifically, she is an Anti-Villain, but a villain nonetheless. Yet, they chose to do a nasty thing to try and shy away from that truth by having the cast completely validate her actions while lauding her with praise. It is most akin to Watchmen, but instead of the other Watchmen taking issue with Ozymandias, they all pat him on the back and tell him, "Great job!"

Which is totally the writers committing to what they like to do, which is write the unexpected. Everyone expected Hydaelyn to be full on villain, so they put, "For the greatest good, the ends justified the means" by her in the script. Of course, since they love writing the unexpected, what happens in Elpis? Well, when you hear about Kairos the first time you think, "Oh, everyone will get their memories wiped. Tragic." But they couldn't resist subversion even in a single instance, so they let Hydaelyn keep her memory.

There are plenty of people who take issue with her, because she was informed and stayed informed. Which should give her the agency to change things, but she opted to still choose the unknown instead of the people she claimed to love.

As for the popularity poll? Oh jee, in a generation where sexuality is an all important, all encompassing facet of people's identity from their surface to their core I can't imagine why a super hot lady would be high in popularity. Whispers: (Same reason as Emet-selch. She's hot, and people want to bang her.)

And I think they still wound up subverting Hydaelyn vs. The Darkness completely. They just chose to ignore that they already had, so her droning on about Hope = Light and shit sounds poetic and motivational. Nevermind that Ardbert already told us in HW that Light or Dark, doesn't matter. It's how you use them. Which Shadowbringers and Zodiark further illustrated. Hell, to even fight with Meteion who is the "true darkness" we had to use Dynamis, the fictional dark matter in order to win, anyway.