It should also be noted that many particularly powerful items floating around the game world weren't made by mortals.
Our character also isn't just an mortal.
What is Artifact?
Its item of expectational property, when some of their parameters is better then similar item but not the legendary origin or have unique effect thats doesn't have any other items, when they have Unique Origin thats described in game and have unique visuals.
Better way to divide artifacts and custom enchanted items its make caps on spell effects so chameleon 100 and Absorb spell 100 will not so easy achieved, then all thats above caps will become legendary and artifacts items.
Completely with unstackable enchants when more powerful will replace lesser one thats will work best.
There is also need more ways to use applied enchants to item, not only constant enchants on equip but also evocation on use, evocation on strike, evocation on parry or block.
No need simplify system even more then it was in Oblivion, better have improved mix of Daggerfall and Morrowind enchanting system with fixed flaws and added additional features.