I finished my first game of Sorcerer King yesterday. I managed to win in a relatively elegant way - by raising mountains in two or three strategic places. It was on Normal level so I assume that everything is much harder on higher levels.
In my game, I have managed to find the SK's fortress relatively quickly. The fortress was located behind a mountain range which divided the map into roughly two halves. I simply raised new mountains in the only two or three existing mountain passes to seal the SK off. It was not expensive - raising mountain costs only 9 mana. From then on, the game was a no brainer. I cleared my part of the map from the remaining hostile armies, made allies with the mnior factions and went for the tower of dominion victory. I saw huge armies of the SK on the other side of the mountains trying to get across without success. I have thrown some Infernos and Pillars of Flame on them, but it was not really necessary.
All the time I was waiting for some powerful counter spell and expecting that some huge SK army will materialize (using some teleport spell) near my cities but noting like this has happened.
Maybe the designers should consider making the "raise mountain" spell more expensive or develop some strategy for SK to counter this situation. Does it get harder on higher difficulty levels?