*Spoilers* Anyone feel joining Emet would have been better

[Cleretic]

Except we can, because the Echo IS part of the game, and the Ancients do have it on demand, AND they don't use it. It's not theory, it's conveniently sidelined fact. The third option isn't presented because it can't be for narrative reasons. For narrative reasons there wasn't even actually a second option. They're not even put on the table, because the narrative has to be obeyed. It's an obvious hole, and you can pretend that it's not all you want. I don't care about what Emet-selch says with regards to our success. Our success was a given, his statement in and of itself is a redundancy (and it more or less highlights that, oh hey, until he died his memory was stilled erased and nobody gave him the 4-1-1 on Meteion. You can't solve a problem you don't know about).

As for Azem. I've got a feeling they're going to keep him as part of referential dialogue. Never gonna find out what Azem's up too.

Okay, if you're going to keep clinging to this, then I'm going to pull it apart.

Your entire argument is hinging on, essentially, the assertion that Venat could have talked her way into getting the Ancients to replicate the conditions that ended up working with the Scions. And you've decided that the reason they couldn't, that you've cut down, is because Venat couldn't get people to believe her, except that the Echo would let them and so the argument is invalid.

Except the game never says that she would struggle to get people to believe her. The reasons she's selective about who she tells are twofold:

1. As Hermes himself spoke about, the only way the world has a chance is if he doesn't know about his hand in the End of Days. He will either lose his composure, or outright switch sides, and that's basically a death sentence for the planet because he's the only dynamis-knowledgeable person in a position of power to act in response to it. So she can't tell the Convocation, or anyone else who would tip Hermes off, because even if they don't tell him directly, he would be inquisitive enough to know something's wrong. Zodiark's existence is an important defense, and so Hermes has to stay oblivious enough to make it.
2. Huge bummer. Most people aren't going to take the news of 'hey the world is going to end in horrific disaster' tremendously well; and in fact, we know for a fact the Ancients as a whole most definitely do not. So she has to tell not just people who can be trusted with a secret, but people who can be trusted with a soul-crushing truth.

She does this, and amasses the group we see in Anamnesis in 5.2. So now your theory poses another question: if she has these allies, why doesn't she just go with them to solve the problem right then and there? Well, again, there's two reasons.

1. There's no way she could have known what they'd need. Remember that Ultima Thule is an enigma until we arrive; it's not even a proven fact that there's anything there. Sure, by the end of Endwalker we know that what it took was eight dynamis-capable people with some Ancient help (well, technically nine, but Zenos kinda just provided moral support and a moving platform), but they had absolutely no ability to learn that.
2. The conditions that ended up succeeding couldn't possibly have been replicated artificially, and perhaps the greatest example of that is Estinien. The rest of the Scions connect with the tortured souls of Ultima Thule in their own unique ways, that would've been a tall ask to replicate perfectly; Y'shtola and Urianger reach out through their lifelong love for the pursuit of knowledge, G'raha with indirect experiences that connect with the Omicrons, Alphinaud and Alisaie with both their intellectual and emotional intelligence. But Estinien reaches out with personally-learned, empirical fact, breaking through the dragon's entirely logically-reasoned malaise with lived conviction and physical evidence that they have a future. The Ancients couldn't possibly have done that, because Midgardsormr was still flying.

Venat couldn't have known how to take these shortcuts. But even if she did, trying to take them would have led to failure that they couldn't afford.

The Ancients, intellectually, weren't fools, even though they might have been emotionally. So it stands to reason that if we can think of a third option, then so could they, and perhaps the reason they only had Venat's Plan Hydaelyn and Plan 'Sacrifice Everything To Zodiark' was because all the other plans wouldn't have worked.