Another point that needs to be stressed is that the primary function of modern unions is to deny workers the right to negotiate individually. What leftists call the “right to collective bargaining” is really a privilege given to some people (union bosses) to negotiate terms on behalf of others, without regard for those people’s consent.
There is almost no “intramural competition” between unions for new members drawn from other unions.
No competition based on union dues.
No competition based on management fees.
No competition based on union pension plans or investment performance.
No competition based on political affiliation.
When one Local acquires the right to represent you, they pretty much own you as long as you hold your job.