Were those 249 years produced in a vacuum? Or did they stand on 1500 years of mathematics and trial-and- error? As a quick example, think of a high-end digital photographic camera; you can certainly highlight the major tech advancements that make it high end, but do you know how the screws were produced? Where the grease used on the gears cone from? How long did it take to get to the state-of-the-art optics? How can you even get composite materials to perform heavy-duty cycles?

Those 249 years of tech were based on the previous 249 years of tech, and so on and so on. That is how it works. Nothing you have "today" comes from a vacuum.

They sure didn't slow down after they passed us.

Not just China but almost all of the world. We have parity in most countries right now. The whole point of the WTO was to do technology transfer and allow the US to double down on high margin, finance parts of business since the manufacturing game had the low fruit all picked and wasn’t valuable property anymore. The exception for the west would be to specialize on optics and silicon, two places China is still far behind.