Based on my own personal opinion and experiences? Fischer random creates a lot of uncertainty in my mind when I play. Regardless of what obscure opening is played in a traditional game I still have a sense of what spaces are likely to be controlled by rooks, where I can anticipate a knight showing up and so forth.
As far as your statement regarding branching factor increase can you point me to some references? Its not that I do not believe you I'm curious at what point the complexity begins to take off.
