The first thing he wants you to do in the process of becoming thane is to bring him a bottle of Black-Briar mead, showing that he's decadent enough to care only about his own amusements rather than the welfare of his people.
Wait a minute. How does asking you to bring him a bottle of ale prove he doesn't care about the welfare of his people? You're a stranger walking through the town of Falkwreath. Why should he be relying on you to help his people in the first place?
(In fact, I believe he tells you at one point that his interest in being jarl is access to perks like fine clothes.) The second thing he wants you to do is kill some bandits ... because they've reneged on their arrangement with him and are no longer giving him a proper share of their take. I would call that pretty corrupt, though it's petty corruption compared to Maven Black Briar.
This is pretty inconclusive as well, since bandits and mercenaries are all lumped together in TES. There IS a difference, but since TES doesn't differentiate except to add one token random encounter with a fellow named "Mercenary" with a broken quest, again.. inconclusive.
I would say Vignar is as good a jarl as Balgruuf, with the same concerns for the welfare of the people of Whiterun and definite plans for seeing to that welfare. Dengeir is certainly a better jarl than Siddgeir, and he has a very canny political sense and no great trust of Ulfric, though he supports the rebellion.
And that's an opinion I would disagree with just based on his putting pride ahead of common sense with his one liner about the empire "shaming us all."
Yes, I like Idgrod despite her not having the trust of her people, but Sorli is not a bad replacement and a ruler that does have the confidence of her subjects is probably going to be able to accomplish more.
Regardless of the truth of this, it's still a wash.