Hanson’s model is an ecological model. It assumes that modeled entities don’t reflect the model and respond to it. With intelligent agents simple ecological modelling may not work. You need to use game theory and strategic thinking.

Assuming intelligent aliens, they know this model.

Assuming stable state alien civilizations, they have countermeasures.

Grabby Aliens might discover immune system against cancer-like civilizations growing without limit. It should hit them early before they are metastasized.

Grabby Aliens might foresee immune system even before they encounter resistance. They might try stealthy expansion, gradual probing first strategy, or modify their behavior in order to survive, .... and so on.