If everything is secret then there is no point discussing anything, cause we have no basis of knowing.
China most certainly has public numbers for defense spending. Yes, it maybe understated but that's why have estimates from SIPRI which estimates China's military budget at 314 billion, less than 1.5% of GDP.
IISS likely uses number of active brigades and satellite imagery to count the numbers in service. It's pretty much the best source of military numbers we have.
China may have made a lot of strides in terms military tech. But they are severely behind in numbers compared to US on many many categories such as fighter jets, destroyer count, submarine count, carrier count, extremely low numbers of helicopters in service. There is a lot of gaps.
Chatgpt said As of 2023, the U.S. Army operates a total of 1,106 Patriot launchers, with 480 actively in service. These systems are deployed across various active-duty and National Guard units, both domestically and internationally, including locations in South Korea and Japan.
That is huge