A.) A better job than if there was no one doing the job at all. There are a lot of shitty, crooked people in the world who are marginally kept in check with the threat of being caught by the police and locked up.
B.) No the rulers are just as likely to commit crimes of opportunity and corruption as the rest of us. They also need to be checked, and/or have a way where if they abuse power they can be removed.
C.) Governance is not a perfect system and until we can all agree on a unified code of conduct and actually stick to that code of conduct there will need to be "watchers". The race hasn't grown up enough collectively to not need watchers.
D.) Yes, regulatory capture happens. Is it fair? No.
E.) What a vague question, what solution are you referring to?
F.) Definitely no.