The way I see is this : people are people( fickle and mostly selfish) and they are the lowest denomination on this planet - Rulers (elected or not), "bureaucrats", common people, history that sets these in motion. People themselves are split between OP's and souled. Each had thousand I's ( Gurdjieff). The ability of ruler to influence every thing ( aka corruption in this context) despite the level of power is limited. Each ruler has to choose their "battles". They can set some example (or try to influence) and only hope people will follow, while safe guarding their seat.Is that always the case though? There may not be many counter-examples: Putin seems to be one and even some of the absolute monarchs or Roman emperors appear to have done a good job. Xi Jinping actually does appear to be of a similar caliber as Putin.
The strategies rulers follow can be clubbed into some "Ideologies"( collection of thousands methods whose definitions constantly change according to the need). At the end of day, it is people's free will( if they are conscious) decides corruption level. There is a "quality" of the soul that also needs to be considered, though we can know very little about it. Each nation has lot of "baggage" of the past that makes survival, influences from the family and surrounding has its influence.
If we consider 4D STS that won last cycle, their need to have feeding ( loosh from souled) for their survival, makes "suffering" continue to happen and "corruption" happens to be word we chose to use describe these mechanisms used. Those are the limitation of this world. If people get what they want (which is not the case in the East), common man's desire for corruption tend to be less. As we have seen in the West, corruption is less at the lower levels but at higher levels, it is high ( like a perfectly controlled system hiding behind all the 'fine words').