The models are effectively identical, until they're not. In particular, they're not identical for the purposes of this discussion. "Until pressure from a ceil

The models are effectively identical, until they're not. In particular, they're not identical for the purposes of this discussion. "Until pressure from a ceiling is applied" is the difference between stabilizing at 9 billion people (a bit more crowded than right now), and growing to so many billions or trillions that the grandparent poster's "no more toilets" prediction would be realistic.