Larian will be balancing combat for a certain size party in Baldur's Gate 3. They have chosen 4. That number isn't going to change based on peoples feelings of nostalgia for an irrelevant aspect of the previous 20 year old installment in the Baldur's Gate Series.
May be irrelevant for you, and that's totally fine. But you don't get to decide what does or doesn't matter to the rest of us. For me, a party size of six IS very much a core characteristic of the original BG games and a very important part of what those games were about. Is it something magical about the number six? No. Rather, it is that the BG games were about going on an adventure with your party. The party aspect of the game was central. Even Swen and Adam Smith said exactly this in their recent interview. And for me, that centrality of the party and all the awesome intra-party interactions you got, or even just having five companions who you took along with you on your adventure and who became like a family to you during that adventure was key to my enjoyment of those games. When than number is then reduced from five to three, that is HUGE reduction in my enjoyment of the party-based experience. And while six is not some magical number, it is very much an optimal number, the proverbial Goldilocks number for party-size for me: not too big and not too small. Four, otoh, is definitely way too small a number.
So bottom, line, this isn't an issue of concern for you. It is an issue of concern for me, and a HUGE one at that. And seems like some others agree as well. So when I write any reviews of BG3 in the future, I absolutely will knock the game for the party size reduction because it is very much a legitimate area for criticism.
To be blunt -- nobody cares about your review of the game. Your demographic - obsessed with a 20 year old installment in a franchise - is on no-one's radar. Larian doesn't care what the obsessed with 20 year old installment in a franchise group thinks. No studio making triple AAA games does.
Gaming has passed you by.
The opinion of the obsessed with 20 year old installment in a franchise group on Turn Based Combat is completely and utterly irrelevant. This is a Turn Based game.
The opinion of the obsessed with 20 year old installment in a franchise group on party size is completely and utterly irrelevant. This game will have a player and 3 companions.
Doesn't matter how many times you post about it, complain about it or stamp your feet about it or how critical it is to your world view. These things are not going to change.
Larian will iterate their game and make changes based on it's performance in Early Access of their paying customers. They make their choices based on in game data and feedback of their customers and ultimately what they think makes for good game-play for a modern Triple AAA game.
The opinion of the obsessed with a 20 year old installment in a franchise group is irrelevant to the future direction of this franchise, unless of course you happen to agree with the majority of folks playing Early Access.