Are Saturn and Jupiter really Planets?

I've been wondering lately what are the possibilities that Saturn is actually the black dwarf of a long dead red dwarf that's accumulated materials enough, as it passed through nebulae and eventually found itself in the accretion disk of our proto solar system, to form a layered surface and roaring atmosphere.

One thing that has puzzled astrophysicists a long time is the speed of Saturn's rotation--fast. White and black dwarfs are supposed to rotate exceptionally fast. The accumulation of materials and atmosphere along with its gravitational alignment with the sun might slow the rotation down enough to make it spin only "really" fast by this point.

Just thinking out loud.