Define "stronger"? Do you mean more extreme (maybe more black) or less likely to have deformities?

I thought it was the first two black pastels (Gulf Coast?) that at the time were reported to be pretty badly deformed. But then again I know I've seen a deformed supper cinnamon. I still wonder with both this and the caramel kinking if why some breeders report it as rare and some common has more to do with accidently different environments than different collection genetics (assuming both morphs always have the tendency as part of the mutation preventing it from being bred out).