Anyway, back to evolution, the science of taxonomy.
For all that, there's a consistency in nature. A pattern. It's out there to be seen.
I don't like semantics and I don't like "It's all in the mind" unless something really IS all in the mind. Some things are all in the mind, but not everything.
Taxonomy is somewhat arbitrary, yes. It tends to fail as you go back in the fossil record to the divergence point between branches. The taxons tend to be based on specimens from farther up the branches where the distinction is clearer.
That wouldn't happen so much if evolution were false. That it does happen quite reliably points to evolution having happened.