1. Are you paid for the value you bring to the company, or are you paid for some function of the value you bring and the market value of your skills? Seems to me the largest portion of your pay is the market value. Collective bargaining is playing with the market value, not the value you bring.
2. "Value you bring to the company" is an odd way to look at most jobs. Like what's the impact on productivity of the 25 engineers in an office if the trash hasn't been taken out in three weeks? Janitorial labor is contributing to the overall income of the company in ways that may not be direct, but ARE real. Same would apply for junior engineering tasks.
3. While I'm a fan of the idea of everyone earning the same hourly wage within a company for above reasons, unions MIGHT flatten the payscale a bhit, but they don't usually result in a FLAT payscale. So you will still earn more based on some ladder - years with the company, title, value you bring, etc.
Although you quoted "Value you bring to the company" I did not say that. Your value to the company is separate from the value you bring the company.
If a company has button that when pressed makes them $1M. A person they hired for that role brings them $1M in value assuming they had no one to push the button before. The value of that person is very low since they can easily find a replacement.
But the past inexperienced me didn't bring as much value as the current me so it makes sense that I made less.