It’s clearly not an argument against unions, only a reminder that they’re corruptible just like any other organization.

I wouldn't say "just like any other organization." Most organizations are authoritarian and workers have literally zero say in the operations at the top. Unions are democratically controlled. This introduces a meaningful difference in corruptibility.

Yes, I don’t mean to say it’s organized just like any other organization, but that it is still susceptible to corruption. Which, again, is not an argument against unions, only something to recognize when organizing and being a member of one.

In my experience, partially. Although I am willing to acknowledge that conditions will certainly vary from union to union and even between locals. In my experience, they add an additional layer of bureaucracy and significant cost to an organisation. They /may/ improve /some/ conditions for some workers. But they will also likely introduce other problems that affect all workers and disproportionately impact the top-performing workers to the benefit of the least performing. As has been noted, this isn't necessarily a problem with unions as a concept, but rather a problem with human nature and adding an additional layer of bureaucracy on top of another bureaucracy with conflicting interests. It will at the very least slow things down and add cost. Whether that is worthwhile probably needs a case by case analysis.

Unions are made up of people, and thus can be terrible.

Corporations are (according to M.Friedman) Sociopaths guided by attorneys who define what's strictly legal, who's sole goal is to maximize profits.

I guess that means there are people in corporations too? Does the transitive property apply?