it’s a significantly smaller leap of logic to accept the Shaw ghost as Anakin Skywalker
I don’t see how it makes more sense for him to appear in a form he never had than one he did.
The way I believe force ghosts are supposed to work is they are either a representation of your soul (which remains whole regardless of missing body parts) or it appears as you see yourself.
Real life amputees often still feel as if their missing limb is there and if you’re like Vader where any limb lost is replaced with a mechanical one that operates just as good as your real one then he would have still seen himself as a whole person and therefore returns as his whole self. If he instead lived half his life without one of his arms then he may well have returned as a one armed force ghost as it’s a projection of his self image.
That’s what I figure anyway.
.Val