I agree that the ring species phenomenon is not evidence of the development of "novel complex phenotype structure", but then nobody with any kind of education in a biological science would ever present it as such.
It is however excellent evidence for speciation, which is both a prediction of evolutionary theory and one of its basic building blocks.
An advocate of creation would be better served by explaining how this phenomenon integrates into the creation model instead of jousting at an imaginary windmill. When the end result is reproductive isolation, speciation is not compatible with the strict view of Genesis "Kinds" advocated by JW's and kindred groups.