I'm a skeptic whenever analyzing a scenario of a 'comprehensive alliance' between Russia and China, simply on the fact that both powers have greater ambitions. From an objective perspective I see both Russia and China complementing each other right now on the basis of the following parameters:
1) Energy security
2) Geopolitical correspondence
3) Strategic consolidation
4) Financial Security
Right now, at the current epoch, China has the upper hand in, well, everything, when comparing the bilateral relationship between Moscow and Beijing. Economically speaking the Chinese have a substantially larger economy, diversified economic portfolio, greater diplomatic clout (SCO, AIIB, WTO, et al), larger population. Russia's only upper hand would be energy supplies, which it has an enviable abundance of, and to which is needed to fuel China's continued industrialization and manufacturing and domestic demand.
Other than that, what does Russia provide to China? Technology? China is able to create its own 5th generation fighter : J31, J20. China is able to develop its own AEGIS destroyers: Type 052 Ds; China is able to develop and field its own air craft carrier: The Liaoning Class; China is able to field its own nuclear submarine: Type 091, Type 093, Type 094. What about space technology? China is not dependent on Russia as the former has an active and productive CNSA (China National Space Administration). Software capabilities? China has proven its capabilities with ALIBABA, Xiaomi, Lenovo et al. There really isn't anything Russia can do (or make) that China cannot do on her own.
So...
Best,
@Nihonjin1051