Sure individual sides could *decide* to implement some sort of congress or cabinet of advisers ontop of the dictator system... but it seems like there aren't really any ways in system to long term prevent the rise of command and control... as the best I can come up with is a ruler whose ideals are somehow more democratic, and hence subordinates would be doing their duty to his ideals by assassinating him if he takes the reigns himself... but even that is only speculation, and there doesn't appear to be a way to force the next ruler to live under a similar system...
One option would be a side where most of the military power is held by barbarians. The Ruler is in effect a constitutional monarch.
He would have power due to ability to change build queues and also loyalty of the general units from the side, but he must keep the barbarians on side.
The barbarians could then all get a vote for the parliament.
It could also include a rule mandating that units are converted into barbarians after a while, so that the king doesn't get to powerful (but not to weak either). He has to be able to handle lawlessness but not have enough force to overcome the will of the majority of the barbarians.
Not sure if this is actually possible, but assuming that units can be sold to other sides, there may be a way to sell units to themselves.
Ofc, barbarians are actually all mini-rulers. Jillian has units under her command. Presumably, a barbarian warlord could have human units as part of the collection.
There seems little mechanism to get to that situation. The magic kingdom could be an example where a Ruler decided to offer sanctuary to casters and then ultimately became dependent on them. OTOH, there is no info on how it is actually ruled. It could be a special side created directly by the Titans as an exception.
Most dictators in the real world don't last forever because if the people mass against them, it is hard to resist. However, in Erfworld, the Ruler can just mass disband a protest that is challenging his power.