> if we truly understood how LLMs think perfectly we could predict the maximum number of parameters that would achieve peak

It's a bit of a strange argument to make. We've been making airplanes for 100+ years, we understand how they work and there is absolutely no magic or emergent behavior in them, yet even today nobody can give an instant birth to the perfect-shape airframe, it's still a very long and complicated process of calculations, wind tunnel tests, basically trial and error. It doesn't mean we don't understand how airplanes work.