I agree that the dex sword at this moment does not quite benefit the sinx class. However the weapons were implemented to even out classes. Sinx already were one of the stronger classes so their weapons shouldn't be as good as some others (however the crit sword matches up to the best weapons). Making this sword into a dagger would be OP in my opinion, specially if used for breaking. Emps break too quickly already (in my opinion) changing this into another emp breaking weapon would get us one step back into the "Only rush to emp and break" kinda of woe in which nobody would try to guard anymore cause the emperium breaks so fast.
In my opinion the DEX weapon should get what it's name indicates. Add dex to it and perhaps some hit rating as well. Keep it as a sword and decrease the luk of the wearer to prevent constant criticals. This way it could be used as a thana or incant weapon without the need of a lot of base dex or a phreeoni card.
Just my 2 cents,
Regards,
Ryuk