Full Daedric gear is the best one can have, yes.
As to the Artifact weapons being underpowered comparatively, I sympathize. However, that's pretty much the way it's been in every single Elder Scrolls game, except for Daggerfall.
Well, correct me if I'm wrong, Goldbrand in Morrowind was one of the best one-hand swords available to the player, so not all of them were underpowered. Anyways, it's fine that some Daedric artifacts in the past series were typically weaker than other weapons of note, like Umbra; however, it's bothersome that if you acquire a Daedric artifact at a lower level, you're passively punished in that items available later - crafted, ebony, etc - will all be much better. Items like the Nightingale armor, sword and bow, despite how cool they are, can really hurt a player that out levels them, especially if they acquired them at level 15 or so.