Magical Sharpness also reduces your ability to fend off magical attacks, which for a straight mage build can be a real detriment. If you are looking at this ring from a melee build then you of course don't get the handicap involved. And, the clever rat's ring, morion blade is comparable since you are reducing a quality and having its opposite intensified in much the same way the ring of Magical Sharpness acts. Ok, not all enemies inflict magic damage, but not all characters inflict straight physical damage. And most armor that a melee build can wear is far better at protecting against physical damage than most mage "armor" is against magic. The equals here might be a dark silver shield and I think the Brushwood shield.
That being said maybe it is appropriate to have a ring that decreases your vitality temporarily and increases your attack power for that time, but that might be too nasty. And those that often use the Clever Rat's Ring and/or Morion Blade do it temporarily for special situations. Mages take the chance all the time that physical attacks will overpower them easily. Melee builds can almost always more easily counter these more prevalent kinds of attacks. The magic power increase is only +20% whereas for the Clever Rat's Ring the attack power increase is +50%.
As Nintendoblivion said every build has its ups and downs.
