Four is a party. Six is the crowd. Five is a ideal party )
6 is better, but 5 is a good compromise for everyone's whish
Not too hard for those that want to play with only 4, not too unbalanced for those that want to mod the game for one more companion slot. And probably a number the vast majority of us would deal with and enjoy.
I'm asking for 6 for a long time but I can reconsider 5 if that suits better to everyone.