I see quite a few people wrongly conflating nostalgia for surface elements of BG/BG2 with the FEEL for how the game plays. The play in a full party of six FEELS very different than running only the player character and maybe one companion. A full party of six provides many tactical options that are simply impossible for only one or two toons to try let alone pull off. While a party of four is better than only one or two, six is even better than four because the more people in the "fireteam" or "squad" the more redundancy the party can have with important skills and abilities. Effective use of small unit tactics is much much more important and actually doable with a party of six instead of only one or two. Granted, four is better than one or two, but not as good as six.
I also see a significant reliance upon people, and Larian apparently, using a false dilemma. Not every member of the party has to be a fully scripted NPC with lots of lines and interactions with the each other and the player character. In addition to the four party members with the full background and script the party can also use two red shirt henchmen with generic lines so they can interact with the rest of the party. Showing respect for the legacy of what came before in D&D games like the Icewind Dale and Balgur's Gate series isn't a bad thing. Does Larian really have to dumb down combat in an RPG by reducing party size and switching from RTwP to TB to appeal to the gamers of today? Sure looks like it.