You're overcomplicating the issue. I say economists are scientistic because their discipline is a fraud, in that it's not as scientific as they pretend. Scientism explains why the fraud persists, because economists envy the natural sciences (and implicitly look down on the humanities). That's it.

You say economics is a real science, which is why it progressed in searching for alternatives to the the utopian Expected Subjectivity Utility theory. But the scientistic envy of physics explains why economists shot themselves in the foot for so long by presuming that a model of perfect rationality would be relevant to explaining human behaviour. What do you know: we're not that rational. Economics is now closer to biology than to physics (via game theory), which is a good thing.

Again, when you say that Adam Smith's and David Hume's theories were imprecise and unempirical, that's another way of saying they were more philosophical than scientific.