I also believe that snowball shouldnt be slowed down, but instead it should be fought by the rest of the factions. With no snowball the game can turn really repetitive, a complete stall that can only be finished by the player. A disaster.
There is a lot of way to stop snowballs at some point (civil wars would be the best one imo).
Also, the momment the snowballing starts can be manipulated. For example I would like to see factions start really really weak; weak enough so they cant even take a town.... then with time, events, laws, techs, traditions etc factions could get stronger and stronger and more agresive. A bit like the final momments of the roman empire, first raids, then migrations, then invations, then usurpations.