Agreed. We should be asking what the machines measurably can or can't do. If it can't be measured, then it doesn't matter from an engineering standpoint. Does it have a soul? Can't measure it, so it doesn't matter.
Sometimes you only have a one-sided proxy. Eg I can't tell you whether Claude has a soul, but I'm fairly sure my dishwasher ain't.
Ironically, the Turing test is the OG functionalist approach. The GP's comment basically sums up with the Turing test was designed for.
(I don't know what Turing's opinion on souls is, and it doesn't matter for that paper!)