I've been doing some thinking and I think union lifetime limits might adequately cover your concerns. If a union is incompetent (e.g. protecting lazy workers,

I've been doing some thinking and I think union lifetime limits might adequately cover your concerns. If a union is incompetent (e.g. protecting lazy workers, is corrupt, is more focused on political ambitions rather than the workers), then the workers can simply vote to kill the union. A five-year lifespan on unions would put pressure on unions to meet their lofty claims rather than the current state of things where it is universally known that unions are a permanent haven for the lazy.