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).
