You can't exactly go as mage or thief as dwarf since your efficiency applies only to other % building bonuses, anything like towers/homes/banks don't really care (% bonuses wise). If you want your efficiency good then you can't exactly draft 70% to be thief without building the corresponding farms/homes or as mage not without sinking towers on top of farms that you need along with guilds that don't at all care about your BE bonus while also being labor intensive.