I get the impression that no single method (genetics, morphology, ecology, geography, etc.) trumps the others in taxonomy. For example, Homo sapiens and Homo neanderthalensis interbred successfully and yet are separate species.
https://en.wikipedia.org/wiki/Phenetics https://en.wikipedia.org/wiki/Cladistics
I'm not convinced it's "clear" :)
Likely the concept of species can't really be truly defined, but works best as a loose concept for organizing thinking about evolution.