is there a way to get a list of all variant metafields and not only the metafields of a single product variant ?

Currently i'm requesting a list of all products what happens very fast, but after that i have to loop through every product and variant to request each variants metafields and that takes some time.

I know u can get a variants metafields in two different ways: /admin/products/productID/variants/variantID/metafields.json and /admin/metafields.json?metafield[owner_id]=85675678&metafield[owner_resource]=variants

i tried leaving the owner_id blank so i would get all metafields of the owner_resource variants, but that didnt work. :/