Endwalker's story had me, but lost me. Ethical issues especially (spoilers)

[Cilia]

The time travel already happened; Argos expresses familiarity with us on our first trip to the moon, while in ancient Elpis he's standoffish until we prove our worth by holding our own sparring with Venat. The Watcher notes he's very shy unless you know him well. Further Venat (as a manifestation of Hydaelyn) mentions "[A] promise made in another time, another age" while you're traveling to Old Sharlayan by boat, which winds up being something she promised you during your time in Elpis.

That said, as mentioned by Elidibus before we time traveled there, nothing we did would have been able to effect meaningful changes in history because otherwise we wouldn't have been there to time travel back to ancient Elpis. Meteion's fall and flight, the Final Days, and the Sundering all still have to happen, and neither Emet-Selch nor Hythlodaeus can remember us, and reality would shape itself to ensure those are all just so - sort of like a reverse Butterfly effect. There may (probably) exist alternate timelines where things did not happen as we observe them, but those lie outside of our ability to observe since we (probably) don't exist in them.

Time travel is complicated, yo!