Normally daggers would be made out of iron, not emeralds or prismarine shards. Really, there should be all five tiers of dagger.
As for your "venom" enchantment, I see no reason why it would be dagger exclusive. Or why daggers wouldn't take sword enchantments.
Well why dosent the sword get to have the impaling enchant, as swords do impale. I mean, you can add it but it wont do anything. Why cant you add sweeping edge to a tool and it wont do anything? Not all enchantments are for everything, not all enchantments are enclusive, it keeps the game interesting.