If I can have access to everything in one party, that removes some of the more interesting choices I have to make.
ive seen comments like this a lot too - but i really dont see how this tracks. How would having 'access to everything in one party' also 'remove some of the more interesting choices'? the player still decides what choices they are making - i dont see how an increased party size would restrict a players decision making or limit their options. if anything, you would have more tools in your bag to tackle different encounters and scenarios. (id even argue youd have more tools so the player wouldnt need to rely or fallback on more of the 'cheese' or exploit like tactics currently in bg3's ea build, but thats an aside)
even moreso (although tbh idk about getting my hopes up for this), if larian plans on having additional origin/npc/merc companions, ideally varied by class/race/alignment-personality/etc., then even with a party size of 6, the player will still run into scenarios where they will need to make 'more interesting choices' regarding which party members among a large cast they will be taking on the day's adventure.
+1 on getting more info regarding the act/companion locks post act 1 tho, altho i think we are on opposite sides of the fence here too - idk if 'burning bridges and jettisoning companions' post act 1 dramatically improves replayability, but i do think this approach is directly tied to the ea's current limited party size and cast of companions. of course this will depend on larians implementation for the game both mechanically and narratively, but locking the player out of content post act1 of X number of acts (og bg had 7 chapters - altho likely wishful thinking for bg3) currently feels arbitrary and like handcuffing the player's experience.