As a repeat small business owner I would say the lack of public healthcare is the biggest obstacle to entrepreneurship and business formation in the US. It is brutal trying to get a company off the ground and not being able to afford to offer benefits, as it puts you at such a huge hiring disadvantage.

Having to pay fractional benefits etc. would not “fix” things, it would just making starting a new business even harder. For big companies it might end some bad shenanigans they pull, but more likely would just result in layoffs as they consolidated to a smaller labor force.