The Reasoning behind The Sundering? (*6.0 Endwalker Spoilers*)

[Veloran]

Except we do have reason to believe that it is that type of time travel, both other instance of time travel in the game, Alexander and Elpis/Pandaemonium both clearly have us traveling into the past of OUR timeline,

You mean except for the times Venat talks about divergent timelines conjoining again, right?

it makes no sense that one of the three instances of time travel in the setting would operate on a fundamentally different nature of time travel,

Why? It produces a completely different outcome. In fact all three major instances produce notably different effects from one another. It may be none of them are the same types of time travel.

[Kordarion]

You mean except for the times Venat talks about divergent timelines conjoining again, right?

Just because you travel into your own past doesn't mean the future has to be the same, if we say that you can change the past and you remain in the new timeline then you didn't return to where you started sure, but that doesn't mean you travelled to a different wholly sperate universe. The convergence could be, and if it happened is, the merging of two branches of the timeline together, two branches that have the same starting point that connects them to their unbranched past. For example I can cross my fingers together into one unit and they still have the same origin point, my hand.

Why? It produces a completely different outcome. In fact all three major instances produce notably different effects from one another. It may be none of them are the same types of time travel.

Because in each example there are different non-time travel related elements at play, in G'raha's case he is actively trying to change the past, something that would most certainly cause a different effect than the others. So of course there will be a difference when human agency and choice enters into the equation, that doesn't however mean that the method is different especially seeing as Elidibus appears to use G'raha's knowledge of time travel, that he learnt from the blood crystal in 5.3, to send us to Elpis the exact same way G'raha used to journey to his past to change the future. So if the method is the same then it has to be something else that cause the differences doesn't it? Also I'm not sure if its true but I heard someone say that the 8UC based its time travel tech off of Alexander which would mean all three methods are interlinked if true.

I think all of this would be so much less convoluted if they hadn't have written the 8UC short story and then we could say that whatever you do in the past changes the future instead of arguing over branch timelines and theoretical multiverses.

[Veloran]

Just because you travel into your own past doesn't mean the future has to be the same, if we say that you can change the past

Alexander would suggest that any changed past is never actually changed and was in fact always that way. Something that doesn't appear to be the case elsewhere where either things are explicitly different and divergent, or at least incredibly muddled.

in G'raha's case he is actively trying to change the past,

Venat was also trying to change the future. So what's the difference? Clearly G'raha's travel at least was fundamentally different somehow - Otherwise when WoL went back to the past you were actually leaving behind a doomed timeline and entering a new one. The entire thing is so borked that I can't even discount such a possibility, because when discussing this we have practically zero ground to stand on for any perspective.

[Kordarion]

Yeah the whole thing is a bloody mess isn't it, personally I put the blame on Shadowbringers as it was the expansion that introduced the concept of being able to change the past, something that never ends well. Thinking on it, to me that is the difference, not something in universe but the meta reasoning of the devs poor decision to mess with changing the past causing any semblance of rules around time travel to unravel into a bloody nightmare.