It's not bad as a model of evolution. In real world evolution the rules are defined (physics, chemistry) that contain the seeds for the possible outcome. The selection is merely: who survives to procreate. These sorts of models have to establish some arbitrary criteria that permits culling, but that's no different than someone in CFD modeling thousands or tens of thousands of atoms and molecules as a single entity and then continuing the model with thousands or millions of those entities. It's still a valid, demonstrative model.