If loot from quests could be better than the best gear you can craft, then crafting would be a waste of the investment.
So yeah, they should be weaker.
You saying that artifacts should be weaker?
Sanguine's Rose and The Mace of Molag Bal were incredibly lame.
The Mace of Molag Bal is pretty damn sweet weapon.
I allows you to steal HP and SP (both which are needed to any warrior) and gives you Soul Steal effect so you can easily capture souls in your soul gems and recharge the mace.
The Rose may be strong, but it's lame and boring.
I would prefer if it had effect which Skull of Corruption from Oblivion had.
OT:Well, they are not bad if you ask me, but some items should've be tweaked.
-Ebony Blade:Just turn it into a proper two-handed weapon, and that's that.
Still, I personally think that it's secondary effect (one which allows you to attack allies) should go to Blade of Woe and replace it's lame life leeching effect (I find undetected attacks way more fitting for a assassination tool like dagger than two-handed weapons which are strictly used for non-stealth combat).
Last, but not least; once you reach max power of the blade, I think that part which says that it feeds on blood of the deceit should be removed.
-Necromancer's Amulet:Now this item is simply pathetic!
It's positive bonuses are nothing special and pretty common, while negative bonuses are pretty hard kick in the balls.
I personally think that that item should allow you to have one more raised undead at the time (so with Twin Souls perk, you could have total of 3 undead serving you).
Of course, negative HP and SP regeneration should be kept in this case.
-Staff of Magnus:Sweet item, but it shouldn't have charges (just like Ebony Blade), and it is perfect imo.
-Skull of Corruption:This item should only be rechargeable with dreams, not soul gems.
Basically, if this staff is empty, it can steal dreams or deal 10 damage (but you can cast it as much as you want - no charges required), but if powered with dreams, it will refill it and it can steal dreams or deal 50 damage for X amount (50 maybe) of casts.
Other items are good as they are, or I haven't tested them yet, so I can't talk.