While I understand the reasons for preferring a larger party, I can't say I think it would be an improvement in BG3.
EA seems to play OK with a party of four; if you expand the party size, I can see 2 problems related to the turn-based combat being used.
- the number of enemies in encounters would also increase, leading to even longer encounter resolution, when some of them are pretty turgid already. This could, perhaps, be alleviated by using fewer, but more powerful enemies.
- increased party size would exacerbate problems with party characters blocking each other, which you can't resolve because of the limitations of turn-based movement. This is less easy to alleviate, as it would mean re-working the game world to have less choke points, many of which are related to the significantly vertical nature of the game world.
i am pro having 6 open slots for your party, which then allows the players to decide themselves if they want to roll 4, 6, or even solo. i agree with the two most significant issues that you cited (which you also go on to provide solutions for), as these are also other common critiques that ppl have cited in other places in the forums without even considering the party size - ie. rebalance combat related encounters (id argue using more 5e based rules would help alot here) and the limitations and frustrations that the current combat movement (and overall party movement control using the dos2 'chaining' system) controls present (not considering how the current camera controls can also compound this problem). im not sure how much feedback we can expect larian to take from these forum posts (idk when the last time we heard from larian was) but i do hope that the concerns and suggestions that you posted are relayed to the devs as alot of folks agree with the points you made (outside of the party of 4 choice )