Daggers don't benefit from fortify One Handed ENCHANTMENTS because if you sneak attack with the dagger perk (x15) plus DB gloves (x15) = total of x30 Damage. Plus the fortify one handed => a LOT of damage early in the game.
One Handed SKILL, on the other hand, does effect daggers. Though it's not necessary to invest in One Handed at all if you Sneak attack with Daggers. I have an assassin with no One Handed perks, who use DB's Blade of Woe (Not even close to the strongest dagger) with Arcane Smithing perk (you don't need any other Smithing perks for the Blade of Woe) and 100 Smithing, with DB gloves (so total is x30 damage). On Legendary difficutly, I'm able to power-attack one-shot Dragon Priests and all Dragons up to Legendary. It took Legendary Dragons down to about 15% health.
It's insane. I'm thinking about going to Solstheim to temperarily swap perks to get up to Dragon Smithing and get Dragonbone Dagger. Because why not? 