I still am not seeing a valid reason to not have a party of 6.
Because there isn't one. It's not by chance that the attempted arguments are always the same recurring ones like "the official manual suggests 4 players" that were already discussed and dismantled dozens of times in this very thread (well, in the constellation of merged threads that make it). Starting precisely with the very reason why that suggestion is made (the tabletop system obviously needs to sound so frictionless as possible from a logistic standpoint when it comes to gather different players around a table) or the fact that there's a significant difference between several human beings interacting around a table and having constant input on what's going to happen and a CRPG, where NPCs have very limited and sparse chances to interject in the player's decision process.
Even in its best and most grounded form, any argument against a variable number of party members is basically a case of arguing that "if you can't have perfect, then nothing is better than good". Which is obviously some disingenuous loaded bullshit.
And this is before even going *once again* over the fact that we are in a goddamn Early Access and there would be NO BETTER TIME to be wildly experimental with letting the players try different things and see what they will tend to prefer at large.