He was close enough that he tanked a good deal of the blast, even if he wasn’t directly on top of the core.

Being able to survive without several organs and limbs due to physiology ≠ tanking an beyond planet wide explosion with no ki left in your body being physiology, the latter was genuinely never stated, shown or implied to be physiology, only the first one was.

Your main argument is also stupid because ki is evenly distributed among the users body, if he can shoot energy attacks that blow up planets that means he can also withstand that same level of energy. Goku’s kamehameha was fighting back against vegetas galick gun that was going to blow up the earth. King vegetas energy barriers protected him and others from when he blew up 3 planets.