You still need to reason and predict physical phenomena. You could run the world on black-box metaphysics if black-box metaphysics has math that works better. How does Platonism help us there?

Not much. That's the problem. If the universe is a projection of the self, that's fine if true, that's valid if true. We want to believe in things that are true even if they violate our sense of phenomenological aesthetics. But if true, I'm gonna need you to manifest me a million dollars or interrogate your soul for the winning powerball numbers tomorrow. I'll wait.