Suppose Apple created a larger M-series cpu that had the same power draw (320 W) and operating temperature (100 C). How well would it perform against this?
For multi core you can just look at AMD Epyc CPUs which achieve great performance by using many (up to 128) relatively low power cores. An all core load pulls around 400W of power.
Like the new MacBook Air, you mean?
But why is this such a silly idea? A rebirth of the Apple x-server. They make excellent performance cores, they have half of TSMC dedicated to them, and developers love them.