The US military tries to sort out the loudmouths from the competent officers. They don't always succeed, but there's an organized process.

China's leadership tends to be promoted step by step. Read Li Keqiang's resume.[1] Promotions are faster for the well connected (the "princelings"), but leaders go through a lot of jobs on the way up.

[1] http://www.chinavitae.com/biography/Li_Keqiang/career