Manufacturing PMI probably loses its leading indicator status once automation becomes more sophisticated. Many of the sub components of manufacturing PMI (new orders, inventories, etc) completely vanish in importance at that point. Considering there is virtually no inflation anywhere in the world at the moment, there's no incentive for businesses to really invest in this stuff at the scale required to really eliminate the human in the loop.

Powell mentioned the Phillips curve because it's been borderline irrelevant for a while now due to unorthodox global central bank policies.