But you cant really argue that with additional party slot (or two of them) your options would be MUCH wider. Can you?
I can't, but I would also argue that the size of the party isn't mandatory in adding variety to a CRPG. Heck, some people are very happy doing lone wolf builds on DoS2. Since there is no best in slot classes for each archetype, you are still able to mix an match the various classes within the party. I didn't have a moment where I told to myself "I feel limited by the interactions between my party members" since the canvas of different builds/specialization/classes is the perfect size to me.