This gain staging thing with virtual drums… oh boy.
Point 1: Velocity (weight). By increasing velocity, you hit the virtual drum harder. Ok.
Point 2: Kit piece trim. This can lower the volume of the kit piece. So you can have a wimpily hit snare sound loud, or a bludgeoned snare sound quiet.
Point 3: Fader. Further adjusts volume, BUT: Fader controls the level AFTER the insert FXs. So if you’re not getting a good level into a compressor or filter or such, it’s better to tweak the kit piece trim, and then reshape the sound from scratch 
Point 4: Parallel busses, sends to Amb3 group. You might think you’re getting an awesome sound out of your snare, and then you realize all the goodness was coming off the Amb 3 bus
Let’s not forget articulation trim too, since we can adjust a specific kit piece’s articulation level there, too. And the new Loudness knob.
Ahhhh… While I do wish there was a magic way to simplify all this, I don’t actually want to. It’s complex stuff, but very much needed. Mixing drums (with multiple degrees of freedom as BFD offers) is not easy.