Well, what I meant with the problem-solving aspects of the quote in question was that, since it is clear the mists existed in some form before the Ascension, the Lord Ruler did something to them to create Allomancy.
You see, my logic is that Allomancy is a result of the mists. The mists allow you to burn metals. I have two primary pieces of evidence to support this:
1. The mists come towards you as you use Allomancy. The mists would need to be present in your stomach to "burn" the metals, so the interaction of the mind to use Allomancy is actually the method of pulling the mists towards you so you CAN use Allomancy.
2. Vin draws upon the mists, which increased her Allomantic ability. Now it seems so painfully obvious. Allomancers are always channeling the mists to use their magic, so if you were Vin, and were suddenly able to channel a lot more of the mists, you could burn more metals.
Hope that made sense... I always worry that my logic is a bit too roundabout to be cohesive.
Now, if Allomancy is the result of mist-pulling and the mists existed before the Ascension, then perhaps a primary thing the Lord Ruler did to the mists was to "enable" them to be pulled. The mists aren't going to do it by itself, or else, we would've seen Allomancers before the Ascension.
You could say the 15th metal (which was unofficially coined "Partum" recently--see the 16th Metal topic) granted Allomancy. But, you would need to burn said metal to gain the Allomantic abilities. It's like the chicken and the egg: how can you gain Allomancy--which if you burned Partum, you would get--if you don't already have Allomancy to begin with?
I can think of two explanations. First, it could be that Partum doesn't actually give with Allomancy with Allomantic burning, but with the use of a different magic system. A second, more likely, explanation is that the Lord Ruler created the metal to pull the mists to an Allomancer (Note that atium is not a real metal. This must be intentional on Brandon's part, so we can assume that Partum (15th metal) and Dispartum (16th metal) can also be an imagined metal). Thus, the Lord Ruler essentially changed the way the mists interact with people.
Or, conversely, the Lord Ruler changed the mists directly with the power of Preservation. It has been shown--and I believe--that Ruin and Preservation act through the mists. Ruin uses the Deepness-mists, and Preservation through the mist-spirit (supposedly). The Well of Ascension has Ruin in it, or Preservation, or both. Either way, the Lord Ruler would have the ultimate way to use the mists by gaining any of those forces.
Since I am utterly convinced that the three magics are based upon the mists and R/P utilize the mists for their will, it can be assumed that R/P can affect the magic systems (because anything based on the mists can be utilized by R and P both). I presume this is how Ruin can manipulate the Terris Prophecies in the metalminds--while it hasn't been shown that Feruchemy is mist-based, it seems to be a logical supposition, and it explains Ruin's manipulation of Feruchemy. Also, Ruin uses Hemalurgy somehow to talk to people with Hemalurgic metals in them. We can only imagine how insanely powerful Ruin could be with Allomancy.
Last tangent: I just thought of a way to defeat Ruin. Vin could destroy the mists. Don't ask me how, but if Ruin uses the mists to perform its will, then wouldn't destroying its most powerful tool essentially cripple it forever? Unfortunately, that would also mean our three magic systems are also destroyed, but at least Ruin is defeated.
Back on task, the Lord Ruler created Allomancy, literally, by bringing out the mists and allowing the mists to be pulled. So, it can be fairly easy to think that the legends for the creation of Allomancers would involve the mists with them. The mists and Allomancy are irrevocably intertwined.
