Which country were you in at the time? Union laws vary substantially by country so I think this is relevant to understanding different unions and people's experiences with them.
Yeah, I have the choice of about 3 unions where I work, all of which are big unions because there can only be one per industry in Australia. All three have wasted way too much time and members' money on vanity projects that I don't want to join.
Don't know about "designed to" but corruption and abuse of power is absolutely a consequence of this, indeed. Almost feel that this was designed to decredibilise unions (which are essential to democracy in my view) because they ended up strongly reassembling mafias: pretending to protect the people while actually only looking out for your own interests...
It was Germany. I put the union in quotes because the direct translation is Works Council.
I think that some software engineers in Germany are covered by the larger unions like IG Metall and Verdi, but my understanding is mostly for those that work in companies that make physical goods like Mercedes, Siemens, etc.