It's not volume output, Fräulein, it's eveness of signal, string to string response and being able to pick up lowest frequencies. That is where the TB Plus is just better. The Bicentennial pups compress like hell if you play hard, which I know many people like, but I prefer that little extra ooomph in a pup "and if I hit the string harder still, the signal will increase in volume, but not change much"-effect. I'm usually a light player in my pick attack, but do like the dynamics of playing louder via added attack (I've had endless discussions with producers why I do not want my bass compressed in the studio).
What's nice about the Bicentennials though is the way they are wired (parallel?) in their original shape and how - unlike sixties or modern Birds - having both pups full throttle will actually create a fuller sound than just the neck pup.