I mean, if you're just saying one has more output than the other, then that comes down to strings (to an extent, more mids will be perceived as "louder"), play style, setup. But, I mean, different basses sound different, too. If you're in the "All 3" setting on a D-Roc, that's going to sound just a wee bit different than N+B in parallel on an NG. There's so many factors, I'm not even sure I understand why the two are being compared.
I'm also not really needing "explained" what a preamp is and does... been around the block more than a handful of times, including my own circuit designs (and failures) along the way.
Also add the the pickups are probably in different spots. I measured my old D-Bird and they were about 1/2” closer to the neck if I remember correctly. I doubt they changed it on the D-Roc
