Labor unions weren't formed to protect employee's pension plans, they were formed to protect employees from unsafe working conditions. They have outlived their usefulness and represent a major inefficiency in any labor market where the unionized workers do not represent a premium brand of labor. IBEW is an example of a "good" union, in which you can broadly expect to get things done better and faster when you hire from IBEW vs non-unionized electricians.
The Chicago Teachers Union, like the NFL Referees, and the Subway Workers, and Sanitation Workers, and a whole host of marginalized labor groups, don't provide any premium branding for their labor; only the NFL Refs have even half a claim to being the "best" available. These unions exist solely to create inefficiency