When BLU was revealed, they specifically said that their damage calculations do not take weapon damage into account at all, and that there is a higher weight on intelligence than other caster's to compensate.
Unless there is testing that was done that I missed, I see no reason to believe that there was deception in that statement.
EDIT: and the weapon damage variance at 70 is so large that a 15% increase doesn't feel like it can cover the difference.
