Yeah, ”species” is a vague concept and so biologists fight an endless war over where the limit goes from case to case, perhaps ocasionally cursing Linnaeus for coming up with the idea of a single ordering in the first place.
Delving into the recent literature might enable you to make a less clumsy critique. Independently evolving units of biological diversity exist. Any accurate knowledge about them, and about all the edge cases and fuzzinesses and genetic phenomena that make systematization complicated, comes from biology itself.