Looking at Selvaria's powers in this episode (and the previous one), it's no wonder if the Darcsens in the past tried and succeeded in developing some weapons of mass destruction... Anybody would if you had an enemy like that.
Furthermore, a wise nation would have sheltered Darcsens later instead of persecuting them and tried to find out their secrets. Kind of like in our world the nazis persecuted jews and thus aided their enemy's, the Americans', science programs, the Manhattan project included.
It would have been a nice twist if somebody could have presented alternative weaponry able to match valkyria powers. Although seeing how the valkyrias really did anything only so late in the series, it would have been neither necessary nor really smooth plot development to introduce extra stuff.