Even if it does have a low rate, its still a good dagger. Whether in the main hand or offhand to RME, its stats are nice and make it good beyond just the occasional one shot kill.
If you look closely, this dagger is actually the blade extended from Plouton's hands during some of his auto-attacks.
Despite the appearance, said auto-attacks are magic damage. Thus, I think a low proc rate on Death is less of a shame than the fact that this dagger doesn't appear to have the non-elemental property of the twilight scythe.