A dictionary definition is just a convenient pointer to help people pick out “the same” natural abstraction in their own world-model. Unambiguous discrete features make for better word definitions than high-dimensional statistical regularities, even if most of the everyday inferential utility of using the word comes from fuzzy high-dimensional[ ]statistical correlates, because discrete features are more useful as a simple membership test that can function as common knowledge to solve the coordination problem of matching up the meanings in different people’s heads.
And that’s why phylogenetic categories are useful: because genetics are at the root of the causal graph underlying all other features of an organism, such that creatures that are genetically close to each other are more similar in general. It’s easier to keep track of the underlying relatedness as if it were an “essence” (even though patterns of physical DNA aren’t metaphysical essences), rather than the all of the messy high-dimensional similarities and differences of everything you might notice about an organism.
“creatures that are genetically close to each other are more similar in general.” is a ‘high-dimensional statistical regularity’ rather than a ‘unambiguous discrete feature’.
For example, water. The word “water” can be used to mean H₂O in any form (in which sense ice is a kind of water), or specifically liquid H₂O (in which sense ice is not a kind of water). If someone says “water” and you’re not sure if they’re using it in the ice-inclusive or the ice-exclusive sense, and ice happens to be relevant to the conversation you’re having, then you might have to ask the speaker for clarification! Fortunately, this doesn’t cause a whole lot of problems among people who are trying to communicate with each other and don’t have an incentive to start a pointless dispute over definitions.
Water is not H₂O, though water always contains H₂O. You need water to live, but drinking pure H₂O by itself can be harmful.