At some point, a population of organisms developed some sex determination genes. Over time, this system developed into the XY sex determination system: sexual dimorphism due to the segregation of sex-determining genetic information onto a single highly degenerate chromosome. I think it's very implausible that this segregation is without evolutionary benefit. The occurence of sex-linked monogenic traits like the example you give here are a side effect whose evolutionary cost was outweighed by the benefit of the development of the XY system. So I don't think this is a good example for the claim you are trying to defend.