With that statement it don't seem like you been fooling with dogs as long as you say you have....there are culls in all performane animals,good genetics help reduce the cull percentage. (no offence intended)
It's just that simple, Genetics reduce the cull percentage .
Like I said it's all about percentages.
There will always be culls no matter how good a breeding program you have or how good a trainer you are.
About the only people that will try to claim no culls are dog jockeys...