2020 and, likely this year too, are aberrations. We should ignore these two years or wait until the aviation markets in both countries return to normal. Chinese aviation market is still behind the US one considerably in a regular year, although it grows faster. In fact, it is not expected to surpass the US one before 2025, as I remember the forecast before COIVD19.
Unlikely for US civil aviation to recovered totally in this year due to Delta variant of COVID-19. Even if they retake the #1 spot in 2022 to 2023, IATA's last year prediction of China overtake USA is actually 2024.
So it will be interesting to see performance of US aviation market in next two years, bearing in mind while US is recovering, China is moving forward from position of strength.
"Air Capacity Update: China officially the largest aviation market in the world
China has become the world's largest aviation market by seats as capacity in the US continues to be cut.
It has been predicted for some time that China will eventually take over from the US, which has held the position as long as aviation has existed, although no one could have predicted it would come this early.
The International Air Transport Association (IATA) had predicted the change would occur 2024; however the impact of the COVID-19 virus on aviation markets - and China's bounce back - brought forward this major turning point.
While the accolade is somewhat bittersweet, and probably temporary, the result does affirm the fact that China's aviation market is beginning to improve after being devastated by COVID-19.
Significantly, the entirety of the capacity in China is its domestic market which makes up more than 95% of the total. "