you cannot be fired for being a whistleblower, so if you 'all the sudden' had performance problems and got fired shortly after whistleblowing, i imagine courts would side with you.
There are lots of things that you're not supposed to be fired for, that people get fired for. Unfortunately, the onus is on the employee, with almost no resources, to prove that the company was lying.
Sure, you can't be fired easily. But what about when it comes time for a raise or promotion? What about when you are interviewing for your next role? It's hard to imagine anyone getting punished for discriminating in these cases, since it's always easy to pin it on other things.