This game is designed around a party of 4 players, and that is fine. To change it to 6 would require the developers to start over on a huge amount of design work, and probably delay the game another 6 months to a year or more, and cost millions of dollars in development. No thank you.
Stick with 4. It works well, and adds to the fun and challenges in strategy when choosing your party members.
Party of 4, please.
This is very incorrect. They already throw several enemies at a party at a time. The challenge rating of a single enemy is judged on a 1v4 basis. These fights are already over the top on their own. They might need to add 1 or 2 tops more enemies to each area. Maybe.