The stance you're taking is one that is dangerous. China has a billion people and a lot of really smart ones.
a) The J-20 does fly, but it isn't fully operational. But functioning prototypes do exist and have fired missiles. If you aren't satisfied with pictures and videos I guess you'll just have to join the PLAAF and become a pilot yourself.
b) China may bad at engine construction and lag in stealth, but they are world class at designing weapons and their operational ability. The PL-12 and upcoming PL-15 are extremely advanced and their integrated air defense is seriously good.
c) China has drops live munitions on regular occasion. They do it during training and during weapons development. Just because the US and Russia are dropping bombs in Syria doesn't mean they are getting good practice out of it. China's aerospace development is far beyond their aircraft carrier development. Don't think that just because they can't project power across the globe that they are impotent. The ability to operate carriers and resupply underway is exclusive to the USA. Literally every other country has to stop at a friendly port to resupply. China threatens plenty of countries within its range.
The thing about war with China is that it's asymmetric, so they don't have to be as good as the USA to cause problems. If China attacks Taiwan (a commonly hypothesized scenario) they have a huge home team advantage while the USA has to drag everything halfway across the world. The USA can't rest because as soon as they are close enough to defend Taiwan they are under 24/7 threat from Chinese subs, ships, cruise missiles, and planes. China gets to use 100% of it's military for that fight, and the USA cannot use 100% because of the long logistical tail.