Just started Shadowbringer but I have a small question (spoiler)

[Iscah]

I do not believe that we are story wise stuck in the First like the Archons are, and can travel freely between the two worlds at will.

My reasons for thinking this mainly come from some things said at the end of the game.

When farewelling the Scions in the post-credits scene as we prepare to return to the Source, they talk like the Exarch would have to summon us again to get us back to the First - joking about him bringing us to the city and not dropping us in the forest next time. Then he has to specifically prepare the portal for us to use.

For that matter, we shouldn't need the portal at all when we can just freely teleport between worlds whenever we like!

And on returning to Tataru at the end... well, firstly she's surprised that you're back, because we haven't been gone as long as she expected, so apparently there was time dilation at work (despite part of the "freely teleporting" handwave being that time was currently synced up between the two worlds). But it also suggests that it's the first time she's seen or heard ftom us since we left, other than getting a message via Feo Ul - indicating we either never went back to the Source, or didn't bother to drop back in and let her know we were okay. And I'd rather assume we didn't/couldn't get back. Again, needing Feo to take a message suggests we're stuck there and can't just drop back to Mor Dhona to say hi.

Additionally, if you go back to the First and talk to the Scions post-game, they remark that they didn't know you'd come back to the First - as established in the earlier scene, the Exarch was supposed to let them know when he was summoning you again.

So, all those things together, I assume the story was written as if we were unable to freely travel. Presumably there are other benefits to being physically teleported there - perhaps we need a physical body to absorb the Light - but I don't think interworld teleportation is supposed to be one of them. The ability to do so is written into the story, but it feels like it doesn't fit the rest of the evidence.

[Rocl]

And on returning to Tataru at the end... well, firstly she's surprised that you're back, because we haven't been gone as long as she expected, so apparently there was time dilation at work (despite part of the "freely teleporting" handwave being that time was currently synced up between the two worlds). But it also suggests that it's the first time she's seen or heard ftom us since we left, other than getting a message via Feo Ul - indicating we either never went back to the Source, or didn't bother to drop back in and let her know we were okay. And I'd rather assume we didn't/couldn't get back. Again, needing Feo to take a message suggests we're stuck there and can't just drop back to Mor Dhona to say hi.

This particular point can actually be different depending on optional small talk, actually (or is addressed entirely, depending on your outlook on such things).

Should you return to the Source after meeting Feo Ul, Tataru's dialogue does change to indicate she's met Feo Ul and that you should go back to the First and let her worry about the Source. The quest in question, "Travelers of Norvrandt" actually changes a multitude of small talks! The Scions have kept many of their allies in the loop regarding the missing Scions, it seems.

Tataru, Matoya, Lambertient and Arenvald all change after this; Lamberteint doesn't quite believe the Scions are in another world, Arenvald worries for Alphinaud, and Matoya asks us to tell Shtola to come visit when she returns.(I do wonder why they've been updating Lambertient since 4.4...) Of those four people, three of them have the same small talk after completing 5.0's MSQ—Tataru's dialogue, however changes. For clarity's sake, here are Tataru's 3 states:

Forename, y-you're back! Have you already finished saving the world!?
...Not quite? Well, if you need to get back to the First, it should be a simple matter of touching the beacon. It's at the same place we found it!

Forename! I was going about my business the other day when a feisty little pixie suddenly appeared and gave me a report about your doings!
It certainly sounds like you have your work cut out for you. So just leave things here to me and focus on getting things done in the First!

Not much to report on our end, Forename. The Eorzean Alliance is still locked in a stalemate with the Empire.
As ever, in the Archons' absence, I'm keeping the ship that is the Scions of the Seventh Dawn sailing smoothly along. I run a tight ship, I do!

Admittedly, I learned this after I'd personally completed Shadowbringers by way of poking around GarlandTools and the like—but I do have a vague memory of checking in on the Rising Stones before Amaurot to see what, if any, diaogue changed and was amused/happy to see at least Tataru's did while the other Scions in the Stones didn't.

Another somewhat fun fact, is that the only other time dialogue on the Source changes is after you slay your first Lightwarden, Temulun (Cirina's grandmother) changes her small talk to the following:

The light within you shines as brightly as before. More brightly, even. But your journey is far from finished. I shall pray for you.

Everyone else on the Source, other than those I've mentioned here, just seem to have a flag for whether or not you've completed relevant quests (the lv80 job quests) or Shadowbringers (the more mundane Scions). The citizens of the First seem to have a multitude of states, typically dealing with whether you've restored night to the area they reside in, if the Light's come back, and if it's Lakeland or the Crystarium there's even more nuance... it's honestly surprising and I'm ashamed to say I missed most of the interim steps!