Would st john's wort help primary amyloidosis?

No. There are no clinical trials that support this. The treatment for primary amyloidosis uses certain chemotherapy drugs.
I doubt it. To my knowledge st john's wort has not been shown to effective treatment for amyloidosis. Amyloidosis is actually a constellation of conditions of various causes that result in deposition of protein fragments in differrent tissues in the body. Any effective treatment would have to be designed to treat the underlying cause of the overproduction of these protein fibrils.