It makes sense for Lae'zel to join Tav initially. At the very least, Tav put up a decent showing on the mindflayer ship and rescued her. But if Tav spends too long doing non-Creche things, then she would definitely leave. Or beat Tav into submission.
It makes sense for Shadowheart to join Tav initially. She is the most "normal" companion; basically a cult member with her memories gone, and thus the closest to Tav. However, she clearly has strong opinions so it's odd that she just lets Tav make all the decisions. At the very least she should be more snarky when Tav makes a decision she disagrees with.
It makes sense for Astarion to join Tav initially. Astarion is completely out of his element, having suddenly been given the entire world. It also makes sense for Astarion to follow Tav; at the very worst Tav is a source of food. At best, Tav is a source of enjoyment and probably the first person Astarion can call a friend in a long time.
Wyll...personally I think Wyll has exaggerated all his accomplishments, so he probably needs Tav's help. I love that he'll leave the party if you side with the goblins.
Gale...if we believe the whole "tadpole+lost of Mystra's favor has reduced me to a measly level 2 wizard," then he possibly does actually need Tav's help. But Gale does have some important goals. If the player doesn't feed him, then he should leave the party. Or at the very least get more insistent, eventually resorting to stealing items from the party. Honestly though, his backstory is too accomplished for this to be believable. He explored the reaches of magic with Mystra and did that whole thing with the Orb...can he seriously not fend for himself? Does he not have better connections (to other wizards/libraries/etc) to have better options than Tav?!??!? At least, he should think of Tav as a peer and not his leader.
tl;dr: The deference shown by 2 out of the 5 companions is sensible in the current version of BG3: Astarion (Tav is his first friend and potential food) and Wyll (useless on his own; also does leave if you anger him enough).
I think it makes sense for all the tadpole hosts except for Lae'zel to stick together. Once she finds out about the Githyanki that the Tiefling encountered she should be off to meet them, and you should have to follow her if you want to see what happens. It doesn't make any sense for her to follow the player around rescuing children from hard-hearted druids, killing the goblin leadership, rescuing Halsin, standing around while you solve moon-puzzles and explore an ancient Sharite temple, etc. when she has a mind-flayer parasite in her head and she knows that her people can help her.
Especially since every time you interact with her, she pretends to be the boss, but anytime you interact with anyone else, she lets you do all the talking.
My issue is less with whether it makes sense for everyone to band together, but rather with how leadership is determined afterward. Even if Wyll is exaggerating all his accomplishments, he still has to keep up appearances as the Blade of Frontiers. He should be presenting himself as the frontman of the group in every interaction. The player could still call the shots by either butting heads with Wyll over it, or by gently guiding Wyll one way or another in an advisory capacity. It doesn't make much sense for Wyll to let everyone see the Blade of Frontiers take a subservient role to Tav the Guild Artisan without so much as a cutscene addressing why though.
Astarion, Gale and Shadowheart all seem less invested in being leaders themselves, but why would they look to Tav the Guild Artisan for leadership instead of the Blade of Frontiers or the Githyanki with an actual promise of a cure? They all have tadpoles that could turn them into mind flayers. When interacting with Raphael, or the Hag, or Halsin, or anyone else who could have some bearing on this life-or-death situation in their lives, one would think they would be invested enough to interject some kind of dialogue. A question or two maybe. Some bit of arcane knowledge from Gale, or some acerbic wit from Astarion perhaps. There just doesn't seem to be any narrative explanation for why they all stand around twiddling their thumbs while the player does all the talking. It makes them seem completely disinterested in their own fate.
It seems like there ought to be a cutscene where everyone votes on whether to seek out Halsin or try to find the Githyanki, and the player has to break the tie. Or a scene where tensions over leadership between Wyll and Lae'zel come to blows and the player has to diffuse the situation with some kind of compromise or beat both of them into submission. Or literally any explanation at all. Right now it feels like the player calls all the shots and does all the talking simply because the NPCs know that they are just NPCs in a video game.
