Because we haven't been given any strong one handed weapons. Dawnbreaker is more or less an undead killer, and Chillrend is leveled, not to mention most things in Skyrim have some kind of frost resistance.
It'd be nice to have something to be a strong one handed weapon that'd be effective against most targets. Not overpowered, but effective.
The mace of Molag Bal.
I'm happy with the existing artifacts, but a few more would be brilliant. Umbra would probably top my list.
I would like some of the artifacts to gain power as you level, specifically the skull of corruption, it's fantastic early on but it's quickly outclassed by the destruction adept and expert spells.