When he says the timelines could have diverged, he is confirming that they didn't. So the past and present being unified implies here that time became deterministic either due to the player or Venat following the events. Elidibus comments on this exact thing-- that a lack of meaningful change leads to the fated events. I clearly said in my post you can believe she lacks agency or you can believe she has total agency, but if she does it means she risks destroying the future we know to exist since the past and present have become unified. It isn't just "oh some magic timeline forms where we still result in the reflections and Venat is a hero". This is why your post is so long because you are avoiding it. You are focusing on everything Yoshi P said except for the fact that the past and present became unified, which conveniently works out for (again) preserving the timeline. Her preserving the timeline makes logical sense, saving Emet makes logical sense, based on the information she has.
I don't know you read their own answers and regard Venat as more than a tragic figure unless again, you get into headcanon. Originally you were all attacking me for implying the Elpis visit may have spawned an alternate timeline, now you're demanding it.
Saying you want another Venat in an AU is your opinion and I have no comment on it. If you think the resources and time spent to make an experience like that would be worth it for the main MSQ that's up to you. I'm not sure about that.
And again I don't even like that it's the same timeline, I think it's stupid. But pretending it isn't what he's saying is a waste of time. It's exactly what he said, he just gave his own reasons for why the timeline stayed the same which are headcanon bc he, like you, cannot come up with a good and practical reason for the timeline to diverge.
As far as Venat, I will also say they provide context surrounding what she did and imply her decision was "very Ancient like huh" which indicates to me, you're supposed to be viewing it as uncomfortable. But they also lend credibility to Y'Shtola's theory and its up to you to decide if it justifies. They're implying there it was a roadblock. They also mention that the disposition of many people who desired to avoid suffering was an existential threat.
I actually think with this is I don't have anything else to say. The writers make everything clear here imo. You have to decide if certain elements are justified. As for why the game and people of Eorzea treat Hydaelyn well, I imagine it's because they give her the benefit of the doubt that she did what she could and made the best decision she could. Assuming she gave no information at all, did nothing, let it all unfold to become a light God is just a take you can have.