Adding the state as a middleman for a huge fraction of all production does not promote freedom, unless your definition of “freedom” is “the unfettered ability to smoke weed and watch cartoons all day”. In reality, if UBI passes, it will be used as an excuse to un-person political undesirables while keeping people with no intrinsic ambition satiated.

How much economic and employment freedom does one have when health care is tied to the current employer?

Fine, but what's the argument that this proposal will restructure the economy in a freedom-promoting direction? What's the argument that this is a move in the US direction, instead of away?