If you are doing injustice in small acts then you will also do injustice in big acts too, Especially if you think you can get away with it. And person’s view & promise about this does not matter, Because as Schopenhauer put it,

supposing that we wanted to know, for instance, how someone will act in a position in which we intend to place him, we must not rely on his promises and assurances. For, even assuming that he spoke honestly, he speaks of a matter that he does not know. Therefore, we have to calculate his actions solely on the basis of weighing the circumstances that he will have to face and their conflict with his character.

But I think person can achieve this kind of purity, by trying to be pure everyday. The reason i believe this is because i read a ancient Indian text called Mahabharata and it talked about a asceticism, Brahman, ashramas, double celibacy(doing sex only to beget children), mahaprasthana(means great journey, when person determine to departs from home and wanders around, awaiting death). It also had stories of benevolent kings, warriors & people showing uprightness. So, l believe, some people have attainted this kind of purity already in history & it’s proof that man can control their desires and take right actions with impartiality by observing Brahmacharya

So your question, if I can be benevolent dictator without being corrupt or not?, yes, I can be but this job is not best suitable for me because of my personality And currently, my time tracking statistics & recent actions are not showing good results.