If I understand Thor’s hammer well enough, it’s not actually heavy, it’s just that those unworthy can’t lift it. A key hook can hold it up because the hammer isn’t heavy, it’s just that “whoever” tries to wield the hammer, may he be worthy, shall have the powers of Thor. Or something like that. A person needs to try to wield it for it to be heavy. Vision wields it.

And to the point about Vision, I don’t claim that he is human, I say he has humanity: empathy, thoughtfulness, love; he shows all these qualities in the movies. Sure he’s synthetic, but I think Robot is a gross oversimplification that doesn’t do justice to the character.