Seriously. Does the word ATIUM mean anything. The Lord Ruler would be untouchable, able to see every attack. So, we have established that the Lord Ruler cannot be hit. If he somehow was hit, he could heal from anything, with the possible exception of the Shardblade cutting through his spine. But, he can't be hit, being a near equal in speed and able to see the FUTURE, comprehend any attack with zinc. Not to mention the god-like abilities of burning atium with duralumin, which would allow the Lord Ruler to know the outcome of the fight before it even began. Vin killed him by being EXTREMELY lucky. With A- Duralumin, A/F Iron, A/F Steel, and A/F pewter alone, he would be the steeldancers equal. But with Atium, it isn't even a fight.