If you form a union and then the company goes bankrupt, or lets you go on strike forever and hires replacements or offshores the work, that hasn't helped you.

If you form a union and the employer is a monopolist, now that company gets even less efficient, and meanwhile now the union prefers rather than opposes the company remaining a monopolist, which makes it even harder to fix the actual problem.

> it's not at all clear to me how we would go about making all the industries competitive again.

The government solution is to enforce antitrust laws and remove the ones impairing competition. You can do this at multiple levels. If the federal government sucks right now, individual states have their own antitrust laws and many of the regulatory capture rules are state laws to begin with.

The market solution is get all these people you were going to unionize and instead have them pool their resources or raise capital to start a competing company. They already know how to do it because they're already doing it right now, right?