Shenzhen scale is so much bigger than Hong Kong

Officially, Hong Kong's nominal GDP was US$424 billion in 2025 versus Shenzhen's US$557 billion. I assert that these numbers severally understate the relative value produced by Shenzhen vs Hong Kong in the same way comparing the USA's nominal GDP to China's GDP severely understates the relative value produced by China compared to the US. I imagine that comparing PPP adjusted GDP values would more closely reflect reality but still even that would understate how much bigger Shenzhen's real economy is than Hong Kong's.