Party of 4 multiplayer = 0 party slots = Absolutely no ability to enjoy the full game because you can't do a single origin character quest because you can't include a single origin character in your party.
Party of 6 with 4 player max = 2 party slots so party of 4 multiplayer CAN enjoy the full game because you can do a origin character quest because you can include 2 origin characters in your party.
+ Less switching out party members + More character banter and interaction + Party can carry more so less hassle with item management (less running back to the merchant to sell)
