That is exactly what unions do. They setup contracts with the employer to ensure protections and compensation using collective bargaining to balance out the power of the employer for the employer.
Collectively bargaining for hundreds or thousands of employees is obviously more powerful then a single individual bargaining against the same employer, especially when you factor in the information and resource asymmetry that exists in the latter situation.
As the article says, that is not the kind of union they set up. They set up a "members only union" which is voluntary to join or not. Either you are unhappy with conditions and need protection so you join for the the support network, or you are happy with conditions but join anyway out of solidarity with the lower classes of employees. https://tcf.org/content/report/members-only-unions-can-they-...
Or not join at all, which is fine, but punching down and across at your coworkers comes across as not being a team player.
Collectively bargaining for hundreds or thousands of employees is obviously more powerful then a single individual bargaining against the same employer, especially when you factor in the information and resource asymmetry that exists in the latter situation.