#hopefully I'm not forgetting about some obscure piece of lore

[tishinada]

This may be old speculation; I didn't start playing until just before the last patches for Shadowbringers were released. But I was rewatching the Shadowbringers trailer & suddenly realized...Zenos had to survive Ghimlyt Dark. And didn't in the original timeline.

In the trailer, it shows the WoL killing Zenos, and it looks like that fight, using that cracked mask to suggest Zenos in someone else's body while showing him in his own so we know for certain who it is. And that's not what happened. *That* was the moment G'raha first significantly altered the timelines, by pulling the WoL out of their body for a conversation, which of course seemed like the absolute worst timing. Instead, I think it was the opposite, G'raha chose that moment intentionally. Because without Zenos, Black Rose was deployed which was what devastated the original timeline

There may have been nudges to the timeline earlier when he grabbed the Scions, but we know those weren't intentional. People like Estinien and Gaius were trying to stop Black Rose production, but they weren't enough. We know they weren't. It was only stopped because Zenos survived to kill Varis, reclaim his body, & stop Black Rose, whatever his twisted reasoning for doing so. So his survival was an important turning point.

Either way, I think that fight at the beginning of the trailer represented the moment the WoL killed Zenos in the original time line. It has no resemblance to what ultimately happened to Zenos in our timeline.

Zenos deciding to destroy the production of Black Rose might even be a bizarre instance of Azem's gift working even on an enemy who had begun to think of the wol as a friend in a twisted way, whatever the WoL thought of him. Certainly Azem's gift best accounts for his surprise appearance in U-T later.

EDIT: OK, rewatching some of the scenes (it's been quite a while since I watched the final Stormblood scenes), I'd confused the timing. That was actually Elidibus-in-Zenos's body, though it's also the battle where Zenos-in-an-elezen body starts trying to get to Garlemald (and he is also fighting with a katana). But I still feel like that's the point that was altered from the original timeline.