Three quick points. First, union workers in Michigan still have every right they had last year except the right to force others against their will to support the union. That is a "right" that by definition takes away someone else's freedom - hence, not a right at all, but a privilege of power over others granted by the State.
Second, in a perfect scenario a union delivers value not only to its members, but also to the employer. Given some semblance of that it's not at all easy for the employer to divide and conquer because disfavoring the union would be against the employer's own best interests.
Third, we already have the system you describe in some ways. In many good non-union electric companies, a third or more electricians are union members because they recognize that the union provides benefits in accordance with its dues. Off the top, the union apprenticeship program is THE best training you can get, combining book learning (complete the apprenticeship course and you'll have at least one two-year technical college degree) with on-the-job training from qualified master electricians who do the job every day. Union membership also gives the employees some power should management ask them to do something dangerous, to themselves or to others, or otherwise unethical. For instance, should management in a non-union shop ask a union electrician to perform a dangerous job without the proper safety equipment or assistance, he will refuse and if necessary, all the other union members will walk out with him. That also protects non-members, since a union member will similarly refuse to allow a non-member to take on unreasonable risks or do something unethical. And union membership pays benefits in other ways, such as setting wage rates (which must still be negotiated, but it provides a reasonable standard) and in continuing education.
If a union provides benefit only to its members at the expense of their employer, it's a net drain on society as it artificially raises wages and kills our ability to compete while merely moving money from one pocket to another. Operated correctly, a union provides benefits to both employer and employee, allowing employees to earn more and have a batter and safer workplace while allowing the employer to deliver a better product, getting real benefits from his increased costs. Legislating away the union's need to provide any benefits to either employer and employee by making sure the union gets its money no matter the quality of its services leaves the union little incentive to anything for either party.