> Performance improvement plans are not for performance improvement. They are for firing employees. Management already formed an irreversible negative view. It is too late.

While this ends up mostly true in practice, I have known people who were able to turn things around after being put on a PIP.

> You cannot win a case against the company. Because a) companies have more resources and b) even if you do win then other companies will mark you as a troublemaker. Getting hired is going to get a lot harder.

There is a flip side to this. The company wants to ensure it has a water tight case against you, to ensure the complaints are dismissed before going to court. Otherwise, if there is any merit to your complaint, despite the company having more resources than you, they do not wish to be tied up in legal entanglements. This is why HR and Management document everything heavily.

I don't have the source handy, but in the US workplace legal disputes is the number one costs to companies.