Or if you think [this game] is TOO easy, than wtf do we need a 5th or 6th party member for?
For fun? So we can more easily interact with multiple companions, especially if Larian does a DOS2 and kills off all the ones we don't choose? To have more flexibility in party compositions? So that more time in combat is spent playing the game instead of waiting for enemies to take turns? Any of the above reasons alone is enough to want a 5- or 6-person party.
Can't agree more. People play games for different reasons. Some like insane challenges, others like the story, character interaction, etc. Some like all the above. You can't please everyone, BUT you can make certain features be turned on/off, and have difficulty settings, so that players can experience it the way they want to. Again, my opinion though.