This makes sense, but the fact of the Lord Ruler allying himself with Ruin does not. Why would he ally himself with someone who wants to destroy the world? After coming to power, Ruin would be his enemy, as it wants to bring Ruin and Chaos. Instead, the Lord Ruler would more naturally ally with preservation, who would help maintain his throne. True, Ruin would more likely ally with him in the first place (He did pretty much completely remake the surface of the earth, and preservation implies resistance to change), but who wants to be stuck with an ally who's going to spend the next thousand years plotting your destruction?
So really, the most logical idea is that the Lord Ruler just used the power at the Well of Ascension, be it Ruin or Preservation (though most likely Ruin) and forced it to do something. However, if we are going to assume that the Ashmounts are intentional creations, then we also need to find the reasoning behind the intent. You don't just randomly decide to throw up a couple of active volcanoes in a perfect circle.
Perhaps, he predicted the effect the ash would have on morale, and used it to control the skaa? He may have just been trying to change the world completely so that people would not remember the "old days," and would be less likely to rebel. This tactic has been used before by new governments coming to power that felt the people wouldn't really like them (particularly in France, but I guess it's because those French tended to go through governments pretty quickly).
So yes, these are my thoughts on the matter.