This is exact my idea. I am really consider my companions origin and actually this has an equal value with his/her class for me to picking which one of them. I am sure about that most of us have got confused when we had to pick a companion.
I want to pick Wyll because ı really like his backstory but also ı am a warlock. So what should ı do because game itself doen't allow me to gather 2 people in same class, 4 people is so narrow and ı need other classes for functionality.

This why ı want 6 or at least 5 character but I am not compulsive about the old games.

It feels like a huge limitation and this wasn't exist in Dos2. We can pick classes of our companions with origin backstory there and then 4 character didn't seem to a insufficient number because ı did not to think about the issues which ı wrote up here.