This isn't an accurate way to frame things at all.
The US doesn't have 1200 F-35s. 1200+ F-35s have been built but the US only operate less than 700 F-35s. There are slightly less than 200 F-22s Let's call it 900 5th gen fighters by end of year.
F-22s are mostly based in the US. They do not have the range to fly into a western pacific theatre.
There are far more F-35s around than J-20s because F-35s entered production many years before J-20. However the induction rate of F-35s into the US armed forces is roughly similar (if not slightly below) the rate of J-20 induction into PLA. If trends continue as is, total Chinese 5th gen fighters in service will eventually catch up to and exceed that of the US. This remains to be seen. However, it is quite remarkable that the US was building F-22s when China was still building J-7 for PLAAF. I think it's worth considering that trend and the progress rather than one single snapshot there being more US 5th gens in service than Chinese. At a moment in history there was around 400 US 5th gen fighters in US service when there was 0 Chinese 5th generation. Now it is about 900 US 5th gen fighters and over 400 Chinese 5th gen fighters.
Both J-35 and J-20 are entering mass production. It can be pushed up if they wanted but China is only spending about 2% of GDP and even western estimates claim around 3%. The US uses about twice that proportion of their GDP and their GDP is nominally higher.
J-20 production rate is far from disappointing. Even pessimistic estimates put annual production rate at around 120 unite per year. That's many many times greater than say Rafale production rate and about equal to F-35 production rate.
I don't care to discuss in this post whether one is better than the other because truth be told no one knows. A person can make an educated argument for either side based on knowledge and half truths but end of the day, this is a question even US and Chinese military planners aren't certain of.
As for J-35 production. Well the production line has started for airforce variant and carrier variant. It's is going to reach rates similar to J-20's which is again, an impressive rate. No 5th gen fighter apart from F-35 involving numerous nations have hit triple digit annual rate. There are more J-20s produced in a month than India has produced Tejas Mk1 in its entire history. I don't think anyone can reasonably call J-20 production rate disappointing with a straight face.
Mark my words. The US will not get into a military conflict with China. The decision has been made. It is clear as day now even with the signalling. There will be years more of pro western youtubers and commentators talking the US up and China down as per usual for the last however long but you can bet everything the US will refuse to get into military engagement. Behind the scenes, they have completely shifted strategy from considering kinetic war options to betting big on engaging with China in economic and industrial competition. The warfront has moved to a higher degree of political war and media signalling. It will try to hurt China via the political and economic spheres, hoping that would slow its military development down similar to how banning Nvidia H100 GPUs was able to stifle Chinese AI industry somewhat. The issue with that strategy is the US is suffering a faster economic decline and has bet all in with AI now. If it doesn't succeed properly and this means beyond just announcing it has created super intelligence, then China will cement its rise further. When it comes to AI, so much of the US AI industry is run by and powered by Chinese born and educated engineers. Even the Meta leak showed about half of its top tier AI talent were Chinese born and educated. Even if US cracks AGI before China and that's a 50% chance, the Chinese AI experts running critical parts of the US AI industry could not be counted to be loyal to the US. The reverse is less likely where China cracks AGI first and it gets leaked to the US.