Yeah but in some sense you can't use any number because we're comparing the incomparable. "Larger economy" isn't a well defined term. And we can't measure it based on nominal GDP because that involves exchange rates and they depend on factors other than economic size.

It could be said that the US was the largest economy when it was 10x the next by most measures, because it was clearly just better than the alternatives. Not so much now (their model still turns out the best per-capita numbers for a large country though).

The more important measure is really who has the economy best configured to win a war. I expect China to be able to out-produce the US at mass cheap components, especially for drones, so for military purposes I'd expect China to have the long term edge in the sort of moderate intensity conflict we're seeing around the globe. Hard to be confident though, and the exact nature of such a war is unclear because diplomacy would be a huge factor.