China is powerful, but has actually been rather docile, historically. They have none of the expansionist instincts that still come natural to Russia–the only exception being a few tiny islands. The US, Great Britain: every superpower in history was more aggressive than China today.
Russia has unfortunately proven that they are very much capable of inflicting some serious harm. They are partly responsible for millions of deaths in Syria, they are undermining 70 years of rather successful attempts to make the forcible taking of territory a thing of the past at least among some nations. They are undermining the singularly successful effort to abolish chemical weapons (both with their support in Syria and their executions in GB). There's some real fear that they could test NATO, and that he-who-shall-not-be-mentioned might be willing (eager?) to let NATO fall apart. That would be an existential threat for every independent country east of Germany, and it doesn't entirely not be plausible as an inflection point that future history books cite as the cause for the next big war.