The unions are democratic institutions that represent the self-organization of working people. If the current leadership of a union is bad (and in many cases it is) it should be campaigned against, voted out, and replaced. Giving up on the idea of a union because you don't like who's been elected to run it is self-defeating.
One of the major differences between US unions and the rest of the world is a ~50 year old legal hangover related to racism. US unions used to be allowed to moderate their support for members (as in “Joe Bag-O-Donuts is a detriment to the company and should never have been hired”). Unfortunately, many unions used that discretionary capacity to refuse to support their African-American members. It went all the way to the USSC, but the upshot is that US unions are required to have a more antagonistic relationship with management because they can’t endorse throwing out dues paying members.
Ok, now what if that is not possible, and the rest of the workers have extremely bad positions, and it is not possible to convince them to change their mind?
Do you understand now why decentralization of power can have its uses?