So much of your argument seems to come from throwing away what we know of characters' thoughts and motivations, only looking at their actions and ascribing new motivations invented out of nowhere, and preferring the most cynical and hateful versions of why they might do what they do.
Your argument seems to be "Venat committed genocide against her people so she must be an evil person who was always scheming and looking for a way to carry this out just because she's evil and wants to do it" when the game provides you with a far more nuanced insight into her intentions and what she perceived herself to be doing. You don't have to agree with what she did (and I don't like it either) to see her goal is explicitly the opposite of genocide. By her own view, she is not destroying the entire race and is not trying to do so; rather, she believes that she is ensuring their survival. Whether she is correct in that belief is a separate question. Saying "she's just trying to get us out of the way so she can go do evil things" only makes sense after you have misrepresented her motives.
Additionally, the Sundering was her preparation for humanity to fight Meteion.
And we did try to warn people about the Sundering. It failed and the universe continues on.
Everything else you're claiming about "why we kept our mouth shut" is again inventing fiction that was never implied in any form in the story itself. We certainly are not directly scheming to have Azem dead for parts, besides the natural fact that we already have their soul and this cannot be changed, but this is one tiny dot in the wider picture of the present-day existence that we know and are trying to save.
It needs to be emphasised that the situation with G'raha is not the same situation we are in, and in both cases it is more than a case of one person offering up their life. (In any case, we need our one life to go defeat Meteion and save the world we do have a chance of saving.)
G'raha was coming from a future that - supposedly - was utterly doomed with no recovery, and so the decision to travel back in time and change events was the only way that humanity as a whole could survive, because they weren't going to at all on the current course. G'raha was willing to give up his life in the effort to bring about that change, but that was because if he didn't do so, the unchanged timeline would lead to the death of everyone anyway.
(As an aside, I think the writers have done a consistently terrible job of driving in just how hopeless the situation needed to be to justify this kind of intervention over simply persevering with trying to improve the post-calamity world - but as the story relies on the claim that things really were dire enough to justify it, the plot makes more sense if you just go with it.)
By contrast, we are coming from a future that is not doomed yet, but it will be if we do not return to it with knowledge of the origin of the Final Days. Because there is still hope, abandoning it cannot be justified, and we need to do everything we can to save it.
When G'raha committed to splitting his timeline, he wasn't just putting his own life on the line, but locking in the destruction of everything that existed in the world he was leaving behind - again, on the understanding that it was already on the verge of destruction with no way to halt it. When we travel to Elpis, we do not have the same mindset, but are seeking to ensure that our world continues. Therefore there is no reason for us to want to risk being locked out of it altogether and sacrificing everything and everyone for the small chance of creating an alternate path for an already doomed civilisation, whose suffering has already been committed to history or we would not exist to go back and witness it.
In short, G'raha's world and timeline had reached a dead end and the only way out was backwards in time. Ours has not.