Q: Has China surpassed the USA to become the world's largest economy by nominal GDP?
A:
No. China has surpassed the USA by PPP GDP, but not nominal GDP. In the global economy and international trade, nominal GDP counts. However, about 70% of the US GDP is services. This means the GDP does not create wealth in the global economy. It destroys wealth in the global economy through wars for the profit of the military-industrial complex. Even though the US contribution to the world economy is negative, yet the US has the financial monopoly position to get a lion's share of the global economy pie. By this standard, of who gets the larger share of the pie, the US is still the strongest regime in the world.
The US cut of the world economic pie is consumed by Americans and used to fund wars worldwide to maintain the US hegemony position. So the US economy is a parasite in the world economy or a cancer of the global economy. It corrupts the US society and morality. It makes the US the mafia in the world's governance.