If workers are "given" prevailing health care benefits by law, then the rest of their conciliary will go down or be frozen. The money has to come from somewhere.
I would rather be paid a better wage, and work for a company with a buoyant pay structure than for a company where a large part of my pay comes in benefits that I do not want, or can find elsewhere at a rate/coverage that suits me. That is my choice - but unionised companies can't deal with that, seemingly. They made bad economic decisions in the past and now want to drag everyone else down to their level.
It's not unionized companies that can't deal with that, it's the unions themselves.
The problem is that workers don't need a union to survive, but unions do need workers to survive.
A union is a business. They sell their services to workers. Unions are big businesses that exploit workers. They only look after workers in so far as it benefits the union.