all good points to which could be added that dynamics in the repetoire don't necessarily pertain to volume level. they can also speak to color and/or density. thus it is entirely consistent to have a densly notated score sounding forceful at a relatively low volume level. For example, the dynamic markings in Cesar Franck's organ chorals simply refer to the degree to which the swell box is closed (p) or open (f), where a lightly registered passage marked f is actually intended to sound at mp at most. this practice was common among french organists in the ninteenth century (franck, saint-seans, faure) who translated these colorist ideas to their orchestral writing, but more importantly to their academic jobs where their influence became pervasive as the new century dawned in paris. everyone was there and it seems unlikely that primarily orchestral composers (stravinsky, debussey, ravel) would have escaped the perception that orchestration might be less about volume than attitude.
the poor wind players with cymbals and trumpets behind them might not think so, but it's remarkable how quiet an orchestra really is from the conductor's (and hopefully the composer's) point of view...