Indeed, the only value of categories in how useful they are. It's clear there's a continuous spectrum of intelligence/complexity. I believe the main reason we're still arguing in circles about what is or isn't intelligent, is that we also have a distinct, ill-defined category called "intelligence" that carries ethical / moral connotations. We don't know how to handle a continuum of moral weight / personhood.

It's useful in many ways to put a thermostat, an LLM, a monkey and a human on the same "intelligence"/"complexity" scale - there are many interesting things to discuss other than moral weight. And then, for discussing personhood, it makes no sense to include a thermostat.