There is a huge difference between 2–3% and zero percent.
Adding 2% to the US GDP is adding 348 billion dollars. Adding 2% to the GDP of the world is adding $1.55 trillion.
Not that this really matters. Economic growth is slowing, but it is still close to the average. Your figure of 10% growth was nowhere near commonplace, and was essentially only because WWII happened.
In fact, doing some number crunching on the world bank’s data gives me an average growth rate of just 3.5% anually for the United States.