Are you sure that's correct? The tooltip for the skill in-game still says that it reduces summon final damage by 30%, and the patch notes says "In Dragon Mode, damage from allies’ summons will no longer be reduced.". Summons definitely feel like they do considerably less damage still in-game when in dragon form.
I'm guessing Ankama meant they fixed a bug that if you had two Osamoda's in the party, and one went into dragon form, the other Osamoda's summon would get a damage debuff? I've never experienced such a bug but that's the only explanation I can think of.