It may even describe what is an inevitable outcome, but, absent compelling evidence, even that is merely conjecture.
Otherwise, there's nothing inherent to collective bargaining that requires any of the features you mentioned. Even "collective" doesn't have to mean collectivism in the socialism/communism sense.
> assembly line type work where workers are literally interchangeable
Anecdotally, I've read the observation (perhaps even complaint) here on HN that employers still have a tendency to prefer their workers be more interchangeable than intelligent or individually productive.
Even if this attitude is minority, but a large minority, it creates an environment where unions seem desireable.
How do you reconcile this opinion with the high-levels of pay and celebrity in the entertainment industry and professional sports? They're all unionized and their bosses make money hand over fist as well.
Collective bargaining is a life sentence of mediocrity for both a company and individuals. However, for 19th and 20th style assembly line type work where workers are literally interchangeable, then I can understand the appeal of collective bargaining. Some guy turning the same screw all day on an assembly line — there is not much room for “excelling” — you either turn the screw when the next part gets to you, or you don’t. Screw-turning doesn’t really have much opportunity for innovation or extra-mile at the individual level. But for a restaurant worker who might be extra nice to a customer or stay a few minutes late to help make the place extra clean or the kitchen worker who reduces food waste by being more efficient — even those “low” level jobs would be harmed by collective bargaining. Jobs that benefit from collective bargaining are ones with extremely minimal autonomy or require an extremely low skill set: just turn a screw. For jobs that actually require intelligence (emotional or intellectual,) collective bargaining is an insult. Unless of course you are poorly motivated in which case it’s a gift.