Did you read the article you linked to? Employer-provided insurance had nothing to do with strikes or unions. It became popular as a way to improve competition in the job market in the presence of wartime wage controls.

And it's arguably a terrible system that we're still stuck with today, with the effect of handcuffing productive people to their desks in dead-end jobs. We'd be far better off with universal coverage that's not tied to employment... and yes, that means better-off economically.