I don't think we should compare China with the U.S. The U.S. Has been continuously upgrading its armed forces since the beginning. Ever since the end of the WWII, the U.S. has been advancing its military technology nonstop. China, on the other hand, only began to upgrade its military in the 1990's. It was lagging behind by almost half a century. With such a massive force (and I emphasize MASSIVE. China needs such a large force because it is a MASSIVE country with a large population and many unfriendly neighbors) that needs to be upgraded, China has to set a priority.
And China has decided that its navy and Air Force need more immediately attention since these branches lagged behind more. Even more importantly, the navy and the Air Force are almost like force multipliers. An army without the support of Air Force and navy is completely exposed. All those world-class tanks will be sitting ducks to enemy choppers, attack/fighters and bombers. thato is why China has been investing huge amount of resources in developing ships and planes. I can safely say that every China watcher has been appalled by how fast they have been churning out world-class fighters, bombers, UAV's, battle ships, CVs, etc.
It is completely illogical to think that China can simultaneously upgrade ALL its army, navy and Air Force equipment, personnel along with everything to the level where the U.S. Is now. It is equally illogical to expect China to accomplish all this within a span of 20 years.
Also bear in mind that China's defense budget is much smaller than that of the U.S., even using the most generous estimates by Western sources assuming that China has hid a lot of its defense budget. So, with such a short amount of time and limited budget, I think it is nothing short of amazing that China has achieved what they achieved up to this point. And I am certain that China is not stopping any time soon. And I think the PLA also agrees that it is still lagging behind in many areas. And it is working hard to correct them in a timely fashion. We just have to give them time.
Again, keep in mind that they have had a limited budget and they have been doing this for only 20 years. Like that old Chinese saying, you cannot become a one-ton giant with only one bite of food. You have to let them eat, one bite at a time.
It's like someone came up to baby Yao Ming 30 years ago when he was only a 3 ft baby and told him: "I am so disappointed at you! How come you are still this little while Wilt Chamberlain is already 7 ft tall???" What can baby Yao Ming say?