That is kind of the crux of the problem, though it's arguably a necessity after 2 expansions of the Warrior of Light being the protagonist. The epic payoff of Shadowbringers and Endwalker necessitated tying them into Amaurot's backstory; now that we've left it behind they're kind of adrift. That said the fact Wuk Lamat virtually monopolizes the spotlight really rubbed me the wrong way, when places like Heritage Found / Solution Nine and Living Memory could have easily had more story relevance for supporting characters like Erenville and Krile.
Aside from epic adventures all but making the Scions a found family, there's also the Fortemps back in Ishgard, who we're all but an unofficial adoptee of. Not being able to say "I have many close friends that may as well be family" was, indeed, a very strange thing especially when you know where Gulool Ja Ja is going with it.
I see Living Memory as the antithesis of Ultima Thule; it's not bad as a final zone, but really, we could use a little more variety than "already dead civilization(s) recreated from memory." It's definitely meant to invoke Memoria, though the presence of other people and shutting it down are markedly different. (Memoria, in IX, is some kind of weird metaphysical space that also leads you back through spacetime to the original Crystal; the whole reason you have to stop Kuja is because if he succeeds it'll cause a temporal paradox and unmake life altogether.) Whether or not it's the nexus of the Final Fantasy multiverse isn't exactly elaborated upon.
I also liked Sphene, even if she was hamstrung by well... not being Wuk Lamat. I also agree that she improved upon Garland (IX ver.) though in the sense that she had feelings of guilt and remorse, but no option except to stay the course. Garland, to his dying word, feels no remorse or regret for what he does, and Sphene being conflicted about it yet powerless to do anything else puts me in mind of Elidibus (only worse, because there's no indication Elidibus would have chosen a different path were he able to). Getting more screentime and a more sympathetic proper introduction helped immensely (Garland is introduced nuking Alexandria right when you think Bahamut's been routed by Alexander; Sphene is glimpsed during the attack on Tuliyollal but isn't properly introduced until you go to Heritage Found, where she's nothing but as kind and helpful as she can be until Zoraal Ja is dealt with).
Compare Garland's dying thought of "Even if I was created for a singular purpose, I do not regret being born into this world." with one of Sphene's being "I should never have been created." The difference in tragedy is damn palpable.
I'm not yet ready to throw my hat into the "It was Ascians! Again!" ring just yet. I can't imagine they would go through the whole Rejoining business if they had the doohickey that could brute force dimensional fusion, but Yoshi-P did say to remember both the Ascians and the Twelve...