While it may be difficult to quantify manufacturing output using a single metric, 4x industrial output sounds exaggerated to me. The most widely cited figures for global manufacturing, which measures industrial value add, puts China at just over 30% of the global total and the US at around 15%. During WW2, US had more than 5x the Japanese GDP and 10x the industrial output. US produced over 15x more steel, 10x more coal. Most importantly, the US produced the majority of the world's oil at the time, while Japan was critically hamstrung by lack of access to oil. I would argue that Japan's oil shortage in WW2 was a more significant limiting factor to Japan's warfighting and industrial capabilities than rare earths would be for the US today.
Using monetary values to measure industrial output is fundamentally flawed because that equates price to quantity.
A bullet is a bullet in a war. An American made bullet that costs 10-100 times as much as a Chinese made bullet does not give America 10-100 more firepower in a firefight as a monetary comparison would suggest.
To do a proper like for like comparison would be impossible without a stupidly complex analysis of core strategic industries with direct wartime application.
But you can do some basic comparisons with easily available statistics. This is why the ship tonnage figures are so much more relevant than value added.
Similar comparison of things like car production, steel tonnage production, electricity generation and consumption, solar installation, industrial robot installations, the picture is consistent and overwhelming in just how dominant Chinese manufacturing prowess is.
And that is still underestimating Chinese industrial potential. Because even in fields like civilian aviation that the US has a dominating lead in terms of units output, if you drill down to components, you will find that Chinese suppliers play a massive role.