Dawnbreaker : Extra damage and AOE damage to undead (including vampires)
Wabbajack: May not be "useful" due to it's random nature but what do you expect from the prince of madness? It is by far the most fun since it can polymorph enemies.
Ring of Hircine: Unlimited werewolf transformations.
Spellbreaker: Shout protection
The Black Star: At the cost of corrupting an artifact you will never have to worry about running out of black soul gems.
Mace of Molag Bal: Damages enemies stanima, magic, and soul traps them.
Yeah, but I did just say that everything in your list except the Dawnbreaker is useful since they're either not weapons or they're the mace of Molag Bal, which retains it's usefulness later on. As for the Dawnbreaker, the problem is that it's no longer useful later on unless on draugr/vampires/skeletons (not like they pose a threat of any description either way) due to it's low base damage. Wabbajack might be considered a weapon, but it still is a bit useful unless you turn your mudcrab into a dremora lord, since it has a chance to insta kill and provide you with sweet rolls or money if lucky.
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Yes indeed, the Ebony Blade (Artifact, not Ebony Sword) has the greatest swing speed of all the 2-handed weapons. It also benefits from 1-handed perks, unless you have the newest patch. Which you probably do.
Without delving into complicated definitions out of either advanced or kindergarden science books, the simple definition of "fruit" is "the part of a plant that bears seeds".
Daedric weapons are indeed, worthless pieces of junk, to put it lightly, in late-game. The Mace of Molag Bal is a slight exception, counting the fact that it can basically recharge itself if you have the Azura Star or Black Star, as it has a soul trap effect. I have a Steel Sword at level 59 that has a Drain Health enchantment with a magnitude of 20 points and it deals more damage overall than the Ebony Blade. But the Ebony Blade is not hard to get, which kinda justifies that, as you don't need to fight anything or travel to distant lands to get it.