Agreed and understood - the vast bulk of reasons that gave Unions validity in the first place no longer exist. We generally have safe working conditions (OSHA and state agencies), employment laws protective towards the employee (ADA, ADEA, COBRA, ERISA, etc.), minimum wage laws for the bottom rung of workers, reasonable expectations around hours and limitations upon eligibility (no child labor). So, yes, about all that a union does now is extract a higher price for labor by way of collective bargaining than would otherwise be in place in a completely free market. The Unions admit as much - see the website excerpt above for example.
However, one thing unions have done which is a valid undertaking is to help lessen the gap between the highest paid workers (C-suite/VP) and the lowest than would otherwise happen w/o union presence. Currently the gap is unreasonably large, but you can be sure it would be even larger without union presence. You can bet your bottom dollar that senior management would elect to pay minimum wage for the bottom rung of workers (rather than a somewhat higher union wage) if it allowed them to have bigger bonuses and declare larger dividends (which in turn generally drive the stock price up and increase senior management stock compensation).
I just don't understand public company CEO's who actually think they're worth 100+ times the wage of the rank and file. It just ain't so.