I already have and use orchestral sample libraries from over a dozen companies, so I don't understand your point here?
If all of the volume settings are the same, VSL's Natural Volume does a very good job, in my opinion at least, of recreating the natural relationship between volumes of the orchestral instruments. It's certainly close enough to allow the listener to hear what a f flute sounds like beside a mf trumpet, for example.
As the relationship between timbre and volume in the virtual instrument is only approximate (if only four dynamics are recorded), the changing relationship between timbre and volume throughout the instrument's dynamic range can not be reproduced with precision; a single velocity layer has to cover a large part of the instrument's dynamic range. This means that there is an inherent compromise regarding the dynamic range and volume for the VI (it can only be right at four MIDI velocities). Within these limitations, I think MIR's natural volume gets very close to representing the volume of the instruments in a live orchestra.
With VI and MIR, it is possible to mix a composition using only MIDI values and stage position, as one would expect if Natural Volume is implemented well. Further conventional mixing may be required to emulate conventional multi-mic recording techniques with spot mics and so on (or for solely artistic reasons), but this is no longer using natural volume.