I can imagine a great many things we collapse to one term because of similarities are in fact distinct, from myriad causes. Cancer is an example. The common cold is diagnosed based on symptoms, but is a reaction to any of several kinds of virus. Hell, a crab or a tree is not one class of things, but many that converged on common solutions.

There’s an ADHD specialist, a neurologist, who wrote a book called “ADHD Does Not Exist”. His core argument is that ADHD is not a single disorder but a collection of symptoms that cluster together from many different underlying causes. https://isbn.nu/9780062266743