Well, I finished the game and it was a strange one.
Every other faction but me and one Cultist faction died by themselves, have no idea how.
I have been sprawling and turtling a bit, playing as Wind Walkers, and the cultist had many villages and a huge army, and started to be really aggressive. I know I could not stop them, they had better stats, and on top of that, their units were counters to most of mine (ranged slayers).
My only luck was having ice wargs that kept me going in winter, because in winter, they were just unstoppable.
However, when the huge masses started to march on my cities, and I was in despair (cultist raze your cities and on top of that, steal your tech), diplomacy have saved me. They laughed at all my resource stockpile, they refused dust, but what it took to secure a truce was - 12 units of spice. It was the only luxury that was in high demand.
So I gave them this ridiculous small quantity of it (I suspect there was no source anywhere, I had around 50 units from quests). And the cultists took the truce, and marched aaaaalll the way back to their distant lands, which took considerable time in winter. Then, after some time, they once again realized they are much stronger, and declared war and marched across the vast empty lands back to my cities. And at the very last moment, I gave them 12 spice. And they went all the way back.
This repeated over and over, until I finished the main quest, built the Temple of Whatever and won the game.
Quite anticlimatic, expecially since there is no faction-specific outro.