The question is whether it's more productive to conquer other continents and plunder them with 18th century technology or just produce stuff with 21st century technology. And it's not as easy as you'd think. Most of the imperial powers spent a
lot of money on things like shipping people across oceans, maintaining vast military forces to guard their empires, building massive amounts of infrastructure in their empires, trying to convert the natives to Christianity or at least stop them from immolating themselves on their husbands' funeral pyres, teaching the natives to govern themselves, getting into wars with your colonists when they want to be an independent country, and getting into wars with the natives when they want to be an independent country. Adding insult to injury, having huge empires means a war with the neighboring European country turns into a huge world war between your colonies and the enemy's colonies. It gets so expensive that eventually you have to abandon your colonies--and it's not like India or Africa just ran out of natural resources. Quite the opposite, really.
So instead of messing around with all of that, China's expenses are limited to building infrastructure in China, maintaining vast military forces to guard China and occasionally menace Taiwan, and converting the Chinese to some vaguely secular state-approved worldview. And they have the benefit of modern technology and the entire developed world to crib notes from. They don't have to figure this shit out the first time. A factory anywhere in the West in the 19th century was a best guess--a Chinese factory today benefits from 200 years of experience and empirical research into how to run a factory, robots, computers, a huge foreign population of people buying stuff, and thousands of Western-educated professionals. I think China has the advantage.