Those suppositions really don't stand up at all though (Edit: this is to mrfuji's comments, I was just slow in typing), not for more than the five minutes it takes to walk from the wreck to the druid grove.
I other party-based RPGs, the player character is the leader because the other companions lack the immediate personal drive or direction to BE the leader - your character steps into that role. this is not to say they're weak or weak-willed, but rather that there is always something that sets your main character's path more firmly than their personal business... and it sets it for your player character more specifically than for them. NWN2 is a good example; your character is thrust into being the leader for your party because their personal objective is the most important thing on the table, and your companions, while they do have their own drives and motivations, were generally treading water or otherwise indecisive about acting, when your character was not... or you brought them on when they had nothing immediate that was more important, and/or they owed you. Larian's characters, however, don't fit and of these reasons, because they are all so uniquely special and powerful and awesome and driven that none of them are followers, and your own character doesn't have anything that sets them apart or ties them to the driving factor of the core story more than the companions. If they do, then it needs to be established right near start of act 1.
Lae'zel, it makes sense for her to let *You* travel with *HER* - but she would absolutely be the one making the decisions, and letting you leave the party if you don't agree to follow her; she has a goal, and a plan, and a hierarchy, and a very specific and overt protocol to follow, and she views all material plane dwellers as lesser creatures, culturally speaking. She would never in a million years simply slip into playing follow the leader to *You* without so much as a conversation about who is leading you. Why has she given leadership of the party over to your character? Why is she unwilling or unable to act upon her own needs and plans, to the extent that she will fall into following another person without much in the way of conversation or challenge? There is no reason. There needs to be one.
Astarion makes the most believable sense, but only until they reach civilisation. It makes at least some believable sense in that he'd accept you making the decisions out of habit, but very soon that habit would give way to really wanting to squeeze the most out of his newfound freedom, and I can't really imagine him willingly following your lead and letting you be the decision-maker at that stage, unless there was something more tangible causing him to do so.
Wyll makes absolutely no sense at all; he's very definitely a cut-your-own-way person, and even in his weakened state, he's got a plan and a goal, and would be unlikely to declare you the leader of the party over himself or his own plans and needs - especially given. Wyll would tell you that he's going to do something, and he'd ask, invite and entreat you to come with him... but he wouldn't meekly say 'yes boss' and follow you when you decide to do something different instead, no chance.
Shadow, again, no chance of her humble deciding that you are the leader of the party, and the one to make decisions. She's so busy telling you that she has pressing business and that it's none of your business ,that the idea of her actually following you is completely ludicrous, unless she really is a whiny, timid, deeply indecisive person underneath her mask - which she may well be, aside from the fact that she's probably an avatar/chosen of selune, or the living incarnated truth of the darkmoon heresy. I'd believe either. Like the others, she's got a very strong sense of purpose and a goal, and that does not gel with letting a random that she doesn't know anything about make all of her decisions for her, even when they're things she doesn't like or doesn't agree with... especially when we decide to do things that expose the party to danger, which she is very adamantly against doing. She'd be gone in a heartbeat after the first few times of that.
Gale... a former archmage, who, though diminished in power, still has his archmage brain, bearing, memories and history. He's definitely not going to be the sort to put someone else as the party's leader. He's absolutely the most qualified to lead the party and make the decisions that need to be made, at least in his own eyes... the idea of him kow-towing to a random nobody that he doesn't know is perhaps the most ridiculous out of all of them.
If there IS a reason that causes the others to feel that our character should be the leader and the one making the decisions, then it needs to be established early on. Current;y the game does not do this, and it makes the whole party dynamic feel ridiculous. It's compounded by the fact that all of the party banter is between each other, and never involves out character, and all of our conversations are one on one, with individuals, as though this were an adult visual novel. we're not just the 'leader', we're functionally the detached, uncommunicative general leader who spends all their time away from 'the rabble' and doesn't associate with them unless it's absolutely necessary... and they all accept that.
This is truth.
