In addition, I rather enjoy having a party that isn't well-rounded. If the tools we have available are restricted, we have to get more creative in the ways that we solve problems - this is a good thing (assuming the game is structured in a way that is sufficiently flexible). If I can have access to everything in one party, that removes some of the more interesting choices I have to make. I'm all for burning bridges and jettisoning companions after act 1 - this dramatically improves replayability.
More creative in a system that limit your creativity a lot*
My biggest fear is that we couldn't really have choices in the final game...
With such a limited numbers of companions (let's say 8 as assumed by dataminer), whatever the party size the replayability will nearly stick to "good playthrough"/"evil playthrough" while your main character is probably going to have a class companions do not have instead of something you really like.
Want a pure evil playtrough ? Don't play a rogue or a fighter because you'll have one as companion.
With 6 (or maybe 5) characters in your party you don't really care if you have 2 rogues.