Is it possible that people are mostly “good”, which allows a minority of corrupt and horrible people to rise to the top?
I suppose. Particularly in terms of brute force. But looking at modern democracy, the level of indifference suggests people are only as good as their self-interests.
I would define someone as good if they are doing good themselves wherever possible. That includes fighting injustices and those proliferating injustices.
Evil tends to amass power when perceived good people couldn't be bothered.
We see it time and time again with the rise and fall of fascism.