10-30% seems pretty high to dismiss

What's more dubious is the ability of a penis you penetrate any of the relevant tissues without also suffering injury. Not that it isn't possible, but no way are you going through the diaphragm with human strength, not without also doing serious damage to the penis they're tough, but they aren't jam-through-a-wall-of-muscle tough

Plus, past a fairly reasonable length, there's a small chance it wouldn't be hard enough. It's already soft on the glans, the giving some cushion. Really big cocks can have trouble maintaining a truly hard erection. Not like it's some kind of definite every time thing, but a cock that's maybe 18 inches long, no way is it going to be fully self supporting. Even guys in the ten inch range get a little floppy at times.

So ramming that thing through even the cervix is dubious. Anal isn't even a guarantee that the cock could tear through intestinal walls. That can happen, but it's rare.