It's clear to me what's missing in these discussions is that four takes away from those who like six, but six does NOT take anything away from those who like four. They can still play their game with four (or less). As for game "balance," you just balance the game for whatever number you decide as the developer, and then have a warning with the toggle to increase party size that says: hey, doing this may make your combat unchallenging. Including choices so different players can play and enjoy their game as they want is NEVER a bad thing. Not ever.