I have to disagree, the Romans were the antithesis of ancient China: outward-looking, mercantile, flexible and curious. Rome, played out differently, seems a plausible candidate to climb the tech tree rapidly. you need capitalism for the rapid technological progress that launches you from fireworks, ornate sailing ships and metallurgy to engines, internal combustion and electricity.
And, in the early Medieval era the Muslim kingdoms of the Caliphate were the most technologically advanced.
Cheers
MC
Early on, they were, indeed the antithesis of China. What I'm contending is that if they had resisted disintegration in the state things were being run, they would have become as inward looking and conservative as the Chinese.
In any case this is even more empty arguing than most alternate history, as the fall of the Roman Empire stemmed from a myriad of factors, and in no small part from their flexible and outward looking nature.
I'm not sure if the Muslim were more advanced than the Chinese, in Medieval times.