You cant be EDP'ed all the time. If you consider a fair pvp duel between a twin fang sinx and a sinx with those two blades( maybe ddp or dds and a highly upped CK and IP) the blade sinx will win hands down. Link and sonic blow or dps with EDP has its downfalls, sonic is useless vs high flee classes, and crit dps can be easily countered. But a steady(non-crit) dps with an unknown element plus soul breakers in between, thats scary. These blades have good uses for pvm too, because of the element and the chance of def ignore. You would not need to run a racial def piercing dagger, you could use another like TTS glad and have HUGE dmg, at least when the def pierce procs.
Overall, i still think that they should be made less easily available