It is something I noticed too and moreover on the main output it seems some non-linearity is also at play.
In fact, with my own intruments, I even lower the volume further with a gain effect at the "instrument" level to avoid saturation when playing several notes together like playing chords, typically on a instrument with multiple groups like a pipe organ with several stops.
However when I send a group output to an AUX channel, it seems to me that the output is more like a "raw" output which might be what you want.