As I remember it in the book, the genes were crispr-driven. Meaning ALL offspring got the new genes. So a modified cat having any offspring with a non-modified

As I remember it in the book, the genes were crispr-driven. Meaning ALL offspring got the new genes. So a modified cat having any offspring with a non-modified cat got these genes. So it's not really out-competing that determines the spread speed, it's outcompeting AND any and all interbreeding.