What I think ended up happening actually is that they based the 6.4 balancing on the numbers from TOP, in which there's a commonly used exploit involving DRK where you kill yourself to be revived by the healer lb3spam for mp refills.

The devs likely do not factor these sort of things in and only quickly look at numbers, as thats the easiest least effort thing to do, which would also explain why GNB got damage buffs.