> Which is why I added the remark "[in countries where unions] do work", not when they are just yet another way to take vacations.

That's not a matter that's specific to a particular country, though. It's inherent in the nature of a union structure (and arguably inherent in the nature of any hierarchical human structure, which is a superset of "unions").

You can find situations like the one I described in any country, not just the US.

Inherent in hierarchical structures, yes, but unions don't have to be hierarchical. See: https://en.m.wikipedia.org/wiki/Anarcho-syndicalism There are numerous such functioning unions throughout the world. Small compared to bureaucratic unions, most under various forms of state repression, but very successful and effective in labour struggles they participate in.