This is survivor bias. That example is only known because it was caught and fixed - there are a myriad of other issues that are unseen by the public that a union could address.

such as ?

I have near 0 trust in the major tech companies (Facebook/Google/Apple/etc.) but amazingly I trust the US government even less. I have absolutely no faith that the US government discovered and solved the salary issues in those companies in any meaningful way

You should see how small my check was for restitution payments. I really don't think that the government fixed the problem effectively.

Well with a union, not only do you get wage fixing, but also union dues!

That's begging the question. You haven't explained why unions would be incapable of preventing wage fixing.