Unions can be bad or corrupt or too large in exactly the same way companies can be bad or corrupt or too large. The existence of such bad actors however does not mean that the very concept of companies or unions is bad.
Although it is in principle possible to have multiple competing unions, it is often forbidden (either by law or union contract) and many companies are anyways small enough market.
Corruption makes you more competitive (e.g. Uber ignoring local taxi laws) and the chicken shit judiciary is extraordinarily hesitant to charge companies (think of the jobs!).
The perfect crime in modern times is to think up some convoluted fraud with your company making sure that it's too difficult for a jury or layperson to explain in terms where it is obviously wrong (e.g creating derivatives several layers of abstraction away from mortgages and exaggerating their risk profile). The prosecutors just aren't pursuing cases which aren't easy wins.