What if I’m just better than the rest? What if I can assemble 45 amplifiers a day when my coworkers can only manage 17? (This actually happened to me, long ago.) it is my impression that a union would not allow me to negotiate better terms for myself. Or am I incorrect?
Technically, you are allowed negotiate, but it is illegal for the company to accept and it is not legally binding, so it is functionally equivalent to it being illegal to negotiate terms for yourself (assuming you want to negotiate, it is obviously better at preventing unilateral corporate abuse as the corporation would be on the hook for tricking you).
I believe you can negotiate if the union lets you, but by default you can not. Also, you can not unilaterally waive union representation either, even if you are not a member, so if the union does not allow it you would need to convince 50% of the covered individuals to change the rules or dissolve the union.
That being said, it is dependent on two things.
Some jurisdictions may only allow for a single contract. I don't know where you live, but in my part of the world there's nothing stopping you from negotiating a personal deal. But it can't undercut the union minimum.
The second is the more important part - does the company want to negotiate with an individual? Most places don't. It costs time, money, and effort to do salary negotiations. Companies don't want to set individual contracts for 500 different workers.
Many unions allow for performance-based pay increases. Furthermore, if you're actually doing better (in a situation like you describe, it should be trivial to prove this), it is likely that the union would help you negotiate a better performance-based pay increase than you would be able to negotiate on your own.
And sure, there will probably be some people who are in unusual positions where they can negotiate more effectively by themselves. Similarly, there are people who would improve their status in the United States if we had a Putin-esque autocracy. Even if someone personally benefits from this scheme, I consider it to be pretty bad for uber wealthy individuals to sabotage our democracy so that they maximally increase their wealth.
That sounds like a nightmare to me.