I mean, talking about what things exist, and what things don't, and what it means for something to exist are things that philosophers do as part of philosophy (specifically ontology). I suppose there's nothing wrong with Deutsch's characterization, I guess we can just call the philosophers who, in doing philosophy, discuss the meanings of words (like what it means to exist or, as Dennett and many other philosophers have, what it means to have free will, or all kinds of other terms) scientists who are actually doing science. If we use the terms this way, the academic discipline of philosophy seems perfectly justified since it's actually secretly scientific (they just don't know it themselves!).

But maybe more seriously (and hopefully more fruitfully), I should ask, according to Deutsch's/your characterization, what would count as doing philosophy as opposed to doing science? I would normally say "the things that academic philosophers do as part of their discipline", but it looks like that definition isn't going to stand.