I think they are tying part B funding to med supps believing since B is funded, technically carriers benefit from it too
That is one way of looking at it, but Part B is currently paid by Medicare beneficiaries, not "pre-funded" by payroll taxes like Part A.
And Part B is not just required for Medigap but for MAPD as well.
Saying carriers benefit from funding B is a stretch.
Providers who receive federal funding are required to participate in Medicare and Medicaid.