Such a ‘definition’ preemptively excludes creation as a possible scientific explanation.
Not at all. If science had failed to find a naturalistic answer then the possibility would remain that god-did-it.
But in the case of finding an explanation for the complexity and diversity of life the results are already in. Unguided evolution is a fact.
If you want to hang on to a personal belief that god used evolution to make the world then carry on but it adds nothing to our knowledge of reality.