Distortion adds volume*, and the Pro3 has loads of it in various places. Feedback can also significantly increase the volume, as can filter resonance, depending on how it's used. There is a healthy amount of headroom in that synth so that it can take advantage of these features, so it's normal that an init patch with all of these down or off would be significantly lower in volume than a patch with them cranked up, that's the nature of a high headroom design and is a feature.
* partly by bringing up the average energy in a signal due to the RMS/peak ratio increasing, and partly by just actually increasing the signal volume to the clipping point, depending on which circuit is used and how the distortion is modelled. Compression is a natural side effect/bonus of this, as any guitarist can tell you, too.