When you look at history of past world wars and european wars between great powers, you will understand the lengths Greats Powers can go to preserve their dominance. Its actually naive to think US will only bring a certain percentage of its force to a fight against China. If US and China fights, it will be world war 3.
That means US will try to use every single leverage it has anywhere to try to bring China down. So, not just active force US has, I expect US to bring back retired F-15, F-16 whatever planes US has in its boneyard.
I expect US to force its European allies to fight as well and I expect some fanatic countries like Poland and UK to join for sure. The ones that dont join, I atleast I expect US to bring all the F-35s, F-16s whatever they have in their arsenal and supply to US.
US for example forced Pakistan to supply artillery to Ukraine. So, in a world war 3 which is much more existential, US might ask Saudis to supply F-15 to US to make up losses.
We need to understand the comprehensive hold US and the western empire has on the world. Every country dependent on US for buying arms or protection is a vassal and US will use that influence during the war against China.
Can China's reserve of older J-7, J-6 compare against 3000 F-15/F-16 coming back from retirement or supplied by its vassals? US has much bigger pool of retired fighter jet pilots than China. So, they can rapidly expand their air force with retired pilots.
Yes, China has more manufacturing capacity now. But US has comprehensive dominance on many countries and it will use that dominance to bring in more supplies and forces. China may not be able to match that reserve force with manufacturing new planes alone.
China is still too weak against US and it comprehensive empire.
Too many people forget at the start of WW2, Japan had both the larger, stronger and more experienced navy than the US. But during the course was the US leveraged its gigantic industrial capacity to overwhelm the Japs, the Japs couldn't keep up and by war's end they were massively outnumbered by the US.
Since then the tables have turned. The US over over the last 30 years has deindustrialised. Trump wants to move manufacturing back to the US, but it's not as simple as he likes, because the US workforce has shifted from manufacturing to the white collar services sector. Moving manufacturing back to the US will mean Jim working his cushy office job in NYC will have to give up his job and go work in a sweatshop and get paid less.
The US MIC is now a highly privatised, profit driven industry where super high end, high tech machines are favoured over simple munitions like artillery shells. Their factories operate on a profit driven principle, where excess capacity is considered wasteful. Their doctrine anticipated the decline of industrial warfare in favour of precise strikes using high end equipmen. The Ukraine war has proven that is absolutely not the case, and as a consequence, the US can't keep up its production of shells or HIMARS missiles for even Ukraine.
By contrast, the Russian MIC is state operated, and their factories are built with plenty of spare capacity on standby so they can massively ramp up production when war comes, and it's paying off in Ukraine now. AFAIK The Russians are outproducing the US in artillery shells.
If Russia is able to outproduce the US, what about China, the world's pre eminent industrial juggernaut which produces everything for the world? The roles have flipped. The US which was the industrial powerhouse at WW2 has now deindustrialised, China has now taken its place. In a way China is now in the position of the 1930s US.
If a war breaks out I predict the US will have the initial advantage because of its stronger military. But if the war drags on, then China's gigantic industrial capacity and population will come into play, and as long as it survives the initial blow, it'll be in a good position to outproduce and overhwhelm the US.
The US navy was weaker than Japan at the start of WW2, but much stronger by the end. China's in a position to do the same to the US with its industrial base as long as its supply chains are secure.