"The preceding guidelines assume that you have a party consisting of three to five adventureres... If the party contains six or more characters, use the next lowest multiplier on the table." - Page 83 D&D Dungeons Master's Guide
5e considers 4-5 to be standard while 6 or more being optional, totally up to the players and DM for party size. So Larian at the very least can give us max 5 party members if they're being picky with the rules. The reason why many players want the option (keyword option), is because it was an option in the original BG 1 and 2. This is a Baldur's Gate game, doesn't matter who's developing it. I also would like to mention that many official WofC D&D adventure modules of both current and past editions are geared for 4-5 and 4-6 players. If you want "lore" to further prove my point, take a look at Drizzt companions. He has 5 total in his party. So what if players wanted to have fun and roleplay as Drizzt in BG3 and (hopefully have an option later to add fully other customize companions) his companions from the books?
I don't know how much more literal I can get with actual sources. I don't understand the issue of not favoring max 6 party members as an option.
Kind of bogus to wait an enemy the size of a platoon (18 - 50 soldiers) against my 4 party members that doesn't even add up to a squad (6* - 10 Soldiers).
If you think that it's "too easy to have 6 party members. Then play with your 4 members or less, you play your game how you want to. If you think the game is not meant for the space of 2 extra party members, I'd beg to differ. Most battles have you against many number of opponents and there is plenty of space for 2 more party members. If a warlock can have their minion and a ranger can have their pet in the same party of 4, It can fit more than four or even 6 playable characters in practically every area. For many of the old-school BG players. Remember Firewine Ruins and how claustrophobic it was? You almost had to move the party in a single file line in that dungeon. BG3 EA hasn't had any dungeons or areas as claustrophobic as Firewine Ruins and if they did, I'm sure it would be a fun, interesting and challenging dungeon. Also, I hope to God Larian fixes the party movement and controls.
Again, these are only options that they player can choose.
I thought that was why we all love RPGs. The fact that we can have more variety to solve which ever situation is always a good thing. I'm sure most of us can agree to that.