About that political power, in some European countries, and maybe most famously in Netherland, a lot of big labour-related economic decisions are made in a committee with representatives of the government, representatives of employer organisations, and representatives of the major unions. They discuss and agree on salary structures, pay increases, labour conditions, and I think they can even make suggestions for changes in the tax system. If all three agree that something is better for the country, the companies and the workers, then it's very likely to happen. Note that these agreements hold for everybody, and not just union members. So non-members do benefit from some things the union does.

But the important part is: they need to balance the needs of all three parties: the country, the companies, and the workers. It would be stupid to sacrifice one of these for the benefit of one of the other stakeholders, as that would ultimately hurt everybody.