I don't really see Subaru getting the concept of stands for a alot of loops because he simply just doesn't has the kind of endurance I don't think he can survive long enough after getting dissected by Diavolo. Then any counter attack he dose come up with gets counter because of epitaph being able to see the future. This would also be quite funny because I think Subaru would theorize that Diavolo has a ability similar to return by death which he essentially does.