There’s was a lot of manipulation of unions in the 20th century that I imagine contributed to things like this. I’m no expert but I know a huge change was the Taft-Hartley Act. This made a lot of significant changes, but one that I can think of is that it outlawed wildcat strikes, which are union strikes without the authorization of union leadership. This change would have the effect of centralizing union power, increasing bureaucracy and weakening the very idea of a union.

So yes historically unions have been a mixed bag, but it is worth considering how much of the negative aspects of unions were created through changes to laws that ultimately destroyed unions (in the USA).

https://en.m.wikipedia.org/wiki/Taft%E2%80%93Hartley_Act