The problem is this. In the original Eighth Umbral Calamity timeline, Azem didn't travel back in time to Elpis because Azem is dead prior to that point. So there's some sequence of events that originally happened on Elpis that didn't involve time travel, and in which nobody comes out with any knowledge of future events. We don't know how that played out. We don't even know if Meteion ever had the courage to give her report to Hermes or if she was ever identified as the true cause of the Final Days. After all, it's Azem's questions about Dynamis and knowledge about the future that lead to the situation being examined more closely and ultimately force the showdown on Ktisis Hyperboreia.

When G'raha alters the Eighth Umbral Calamity timeline, it creates a new timeline that diverges from the original. That raises a flag that actually allows for the time travel event in Elpis to actually occur in the first place.

As long as key historical events remain unaltered by Azem's time travel journey, you now have a nice closed loop that replaces the original sequence of events without any net change to the past. This is an important distinction, because you still could conceivably alter something in the past that only had relevance to an event that hadn't yet happened, such as your showdown with Meteion in Ultima Thule, while still keeping the original timeline intact. If there is a net change to past events, the timeline frays off into a set of divergent timelines depending on what changes. As Venat notes, Kairos fairly important, because the memory wipe allowed a conjunction to form between the two Elpis timelines. If Emet, Hyth, or Hermes retained their memories, the present would likely be significantly altered as a result.

Now there's the question of whether there are consequences for splitting a timeline. It seems convenient enough to be able to just rewrite events at will and ignore the frayed ends. For example, Elidibus explicitly warns you against trying to prevent the Final Days. Is there a reason why we couldn't just do what G'raha did in this instance, and more to the point, are there consequences that we'll have to pay down the line for splitting off the Eighth Umbral Calamity timeline?

I don't think that Azem predicted that they would be time travelling back to Elpis. It's also unlikely that Venat told Azem this. The most likely explanation is that in the original sequence of events, Azem told Themis to wait for their signal to explore Pandaemonium, and then the two of them headed off inside to explore it together. This time around however, you've messed up the sequence of events by showing up and meeting Themis in past!Azem's place, which probably places the present in jeopardy unless you can find a way to reconcile the two timelines.