The main plot went hard for the "Great Filter" hypothesis with a dash of Third Body Problem - I loved the 90 dungeon and Ultima Thule where you basically get to view different civilizations and learn how they came about their end - plague, basically making Skynet and being wiped out by AI, a super advanced immortal race realizing they cannot prevent the heat death of the universe and falling into despair, a race that set their goal to be the ultimate power and turning themselves into machines and then achieving that goal and unable to change their goal now due to becoming machines, after effects of a war causing terminal birth defects that results in an extinction, some enlightened race that loses all meaning due to utopia and literally creates a death mechanism to escape their now meaningless existence. Hermes creating a linked "AI" to find what brings meaning and happiness to the universe, but them only discovering death and dead civilizations that failed to pass the filter, and it driving them into madness, like some Lovecraftian plot. It was dark as fuck and I loved it. On a side note, they really should consider making the Omega raids potentially MSQ required. While you can still follow along if you haven't run them, it ties in pretty heavy to that story.
Traveling back in time I never expected - gave me major Chrono Trigger vibes, it felt very Kingdom of Zeal. On that note, I'm kind of confused on what their model for time travel is in this game. Alexander Raid and Endwalker almost seem to use a pre-destintation paradox model, but Shadowbringers seemed to use multiverse with Crystal Exarch altering time. It kind of annoyed me and I do wonder if they will ever address that. I suppose maybe they could use some Doctor Who "fixed point in time" explanation - you can alter time, except fixed points. Although the short story for Shadowbringers shows the future that Graha left still exists, just diverged from our altered timeline.
In any case, it felt like a satisfactory conclusion to the main story. I do wonder how they will handle future stories. I suspect they will be much shorter in scope to avoid ultra-epics, although I wonder if they will have multi-xpac spanning core stories that will still play a role.