Assassins vs encampments & unassigned Commanders?

Other past posts in the forum have suggested that even in cities Assassins only kill Commanders assigned to armies, so in cities unassigned living commanders are safe from Assassins.

What is the current status of all this? 

If Assassins can kill unassigned commanders in cities and kill commanders in encampments, then Assassins become the most powerful units in the game, do they not? PvP battles would then become mostly battles between hundreds of thousands or millions of Assassins, whole cities everywhere would produce nothing but Assassin armies. Commanders would become largely irrelevant, as in most serious battles they'd end up dead before the military battle started, or not fight because the attacking Assassin army had failed to kill them and had gone off to spawn more millions of Assassins before the military attacking could begin.

If the game is supposed to roughly mirror medieval society and armies, then this would be a serious unbalancing of the game structure - if my assumptions are right, which they may very well not be!