That the questions asked by metaphysicians should simply be left to physicists is not a criticism that those not generally skeptical of philosophical inquiry should take seriously. As philosophers, we tend to value the methodology of our own discipline and (whether justified or not) think that this methodology can make uniquely valuable contributions. Philosophy of language should not be abandoned for linguistics, aesthetics should not be abandoned for art criticism and art history, philosophy of mind should not be abandoned for psychology and cognitive science, and so on. There are often more empirical disciplines concerned with the same subject matter, but that doesn't mean the philosophy is in bad standing. Or so say the philosophers, anyway.
Barnes fails to address a missing alternative: that metaphysics should be informed and constrained by relatively up to date physics (and other sciences).