i think that it was not always the case that all the scales were equal
this is reflected in instruments that can only play in certain keys (trumpets, horns etc)
equal temperament was the shoe horning of all the different keys characteristics into a standardized system, prior to the classical period of music
highly fascinating as this all is, my music theory unfortunately peters out at about this point. i'd love to understand this better
i think the 'characteristics' of each key have kept on being associated with them even today, even though they don't really apply as they did, as well as you correctly say the characteristics of the root note
perhaps someone more musically knowledgeable can help me out here