Then the awful rules can be challenged in a court of law, which will act as the limiting power on the SEC. There does exist a mechanism for challenging malicious prosecution in our legal system, and if the corporations feel they are victimized, they can use it.

The point, however, is without antagonistic checks and balances in place, you will always run into the "revolving door" problem.

Challenged how? In legal systems like that of the USA, the regulators can make new laws. You can't indisputably break a law and then challenge the law itself unless it's unconstitutional, but the constitution has very little to say on the topic of financial regulation.

They should disperse that cash to the taxpayers.

Well that's what they do now. The only fines that go to people are whistleblower cases and they get a percentage (and aren't government employees in charge of making the rules!).