I'm an idiot and I have no idea about physics, politics, laws or nature or any of that bullcrap... so someone help me out here:
Let's just say (for the sake of the argument) that Kill-All, the Last Son did in fact weigh as much as a star – which is why Luthor couldn't really handle him... Instead of, you know, Last Son simply being physically stronger and pushing back against Luthor.
But let's say he did weigh as much as a star. And he was on Earth. Wouldn't that have pulled plenty of characters into him? Because as far as I believe to know, a star has a much stronger gravitational pull than the Earth. So, if he did weigh as much as a star (and pretty much was a humanoid star), someone like Batman would have been stuck onto him 24/7 (probably worse than that).
The argument seems to be, that since Luthor couldn't handle Last Son (despite Luthors black hole powered suit), Last Son was as heavy as a star. But other than that there is absolutely nothing that hints at Last Son being an ACTUAL sentient star. Things would have automatically happened at that point.
In my eyes Luthor couldn't deal with Last Son, because he is weaker than Superman – and not because Last Son was too heavy for Luthor to handle. Also, having a black hole powered suit does not automatically mean that everything your suit does equals a black hole. And then when Luthor did release the black hole shenanigans... didn't Last Son die? Or did I miss something? I mean... I've seen Savage Hulk overpower black holes before :-7
My vote goes to Hulk by default, because it's much more clear cut. Hulk was pushing back against the actual weight of a star. Supermans showcase was rather iffy. At least from what I can tell. Feel free to prove me wrong.