The question is complicated somewhat by the fact that often those who seek power, particularly absolute power, are those who would use it selfishly for their own ends anyway. If someone wants to become an authoritarian dictator, succeeds in becoming one, and then starts to act in a corrupt fashion, we can't really suggest that it was attaining the power that made them behave that way... they were already that sort of person.
I'm not clear on that, and as you say it's a complicated question. On the one hand I think you are at least partly right, but I also think about the saying: "opportunity makes a thief" which, I think is also at least partly true and I think it is along the same lines of the sentence mentioned above:
There is a popular saying that power corrupt, but absolute power corrupt absolutely.
So it's not all black or white.
Who defines what is "absolute power"? How do we know when to draw the line to know when an "absolute power" corrupts?