Is there any reason why China is not producing 9000+ ton displacement destroyer/cruisers?
052C and 052C will all be somewhere around 7000 ton. Do they have problems with the engines which prevent them from producing bigger ships?
Engine problem probably is still the main bottleneck. However, Chinese military had been conservative in their modernization throughout history. It's possible that they were just cautious.
When building big war planes and warships, bigger displacement doesn't just mean bigger hulls. There are a lot of other factors influencing the final outcome. I'm sure there are a lot of technical challenges that we don't know about. If it was so easy making ships bigger, the French and the English would have probably already built countless 10,000+ ton destroyers/cruisers.
Judging just based on personal experience, even just modifying a car takes a lot more effort than people think it would take. When putting in a bigger engine, the internals have to be gutted for space, fuel pumps have to be replaced to keep up. The radiators have to be upgraded to cool the engine. Lubricants have to be changed. Usually turbos have to have special exhausts. With the added power, the chassis then has to be reinforced, or else it could deform under hard accelerations. But these are just for straight speed accelerations, if you want any real cornering performances, you would then have to get racing suspensions and high end tires.
Just modifying the car alone could take a team of engineers a year or two (eg. AMG for Mercedes). When even a simple car takes this much effort to modify, can you imagine enlarging and improving/upgrading a billion dollar warship?
Modern marvels like destroyers and aircraft carriers don't just pop up by rubbing the Aladin's lamp. They are sweat and blood of countless engineers. It's ridiculous to hear rumours from Chinese fanboys saying that two/three 100,000+ tons nuclear aircraft carriers are already under construction in China. They simply don't understand the difficulties and challenges in those projects. If they were so easy to build, then every country would have a few of them.