If its WW3, they can basically get every single US made F-35 in the hand of European allies and use them against China. Those allies will happily supply everything they have to US. As far as fielding them is concerned. Every highway can be an airfield. Every large factory or warehouse could be a hidden F-35 hanger. When there is a war, there is a way. The question is how willing US is to fight China. If its full-scale WW3 style commitment, then they are bringing their entire alliance.
This lopsided situation could improve if China starts building 50+ J-35 along with 100 j-20. Then they can probably atleast be equal to US stealth fighter numbers in 10 years. But still won't improve the situation when it comes to US bringing all the allied planes, missiles and other weapons. For China to match that alone will likely take about 2050.