I think the balance is out of whack on most factory default Performances because most arranger players are not pros... they want to hear themselves loud and clear over the backing (takes real skill to get used to hearing what you are playing WITHIN a mix rather than on top of it) and few of them have a consistent and firm finger strength, hence they play much softer than most pros.

But there's a simple solution... Most arrangers have a Keyboard/Style balance knob or slider somewhere easy to get to. I generally back that off at least 30% or more, then jack the Styles' Drum and Bass Parts up a hair if I have to. That's a lot easier and quicker than having to edit every bloody style individually!