He's not as durable.... because his fingers are phased into Hulk's head. He's not at the same density.
Because he is phasing.
It's literally shown - so yes, there is proof. The proof is that he is intangibly going into Hulk's head, without finger sized holes in his head.
It's shown.
But all this is by the by. You asked for a character to stand in one place whilst a recent Hulk incarnation punches him. Abhi showed such a character.
What happens after is completely meaningless and moot. All that matters is that Vision did what you asked for.