A magic-based origin is just what makes the most sense for Billy and Tommy, IMO. There's no other way to logically explain their crazy origin story. Billy inheriting powers derived from Wanda, Tommy inheriting powers derived from Pietro (and even his white hair), Billy and Tommy looking like identical twins... all of that while NEITHER of them are biologically related to each other or to the Maximoffs. I really don't see any logical genetic explanation for all of this, even using ''Marvel Science'' as a standard.
Anyway, here's the cover for Death's Head #4 without the logo in case any of you wanted to appreciate Billy's face.