From the very beginning up to release 4.0c I always found that the factory styles and instruments lack balance, in 2 ways:
1. Some of the styles are much louder than others, e.g. techno, rock&roll, compared to a piano ballad (I am not comparing the reachness of the styles, but the loudness).
2. Playing e.g. a rock&roll style with a solo instrument, e.g. a night sax or trumpet, the solo instruments are not loud enough (imho). Playing the same style together with a string / synth sound works fine.
For me personally this was never a problem, as in a gig I use well-balanced registrations. Eeach song has its own registration, also considering whether I just play or also sing. I do not play songs for which I have no registration ready.
However somebody who wants to react to a sudden wish from the audience, i.e. select on the spot a style and an instrument, might not be happy with the factory balance.