FriedRiceNSpice
Major
The civil service examination system is not equivalent to institutionalized meritocracy. It was an institution created in an attempt to solve the problem of preserving meritocratic governance over successive generations, and despite being the best solution conceived to date, ultimately failed. The system may have worked for the first half of a dynasty's lifespan, but would fall apart due to corruption, bribery, and the purchasing of offices.There is a difference based on what your parameters of "meritocracy" are. If its simply recognizing someone for their talents and giving them a job commensurate to their talent, then every society in the world had meritocracy and China was not unique. Any general on the field can recognize a brave soldier and give them an officership, after which they rise through the ranks and likewise any court official can recognize a servant is sharper than they look and teach them to read/write, after which they begin their ascension through the court. What set China apart from the rest of the world was precisely its examination system.
My history on classical Greece is hazy, but for Rome people only had two avenues to reach a position of power outside of being born into it. It was either joining the military or being sponsored by a member of the nobility, ie. patronage. So yes, in essence "meritocracy" was practiced, but the nobility were the ones having final say on who would rise unless you were charismatic enough as a military leader to lead your own coup.
What set China apart from Rome during periods of dynastic collapse or barbarian conquest, was that by basing promotion on the examinations and creating a class of bureacrats, meritocracy was institutionalized. Successive empires after Western Rome collapsed claimed to the be the new Rome, but never emulated its system succesfully. When a successive dynasty overtook the previous or if the barbarians after finishing their conquest settled down to rule, they had a complete guidebook already laid out for them on how to administer the realm.
In theory, China during and after the Tang dynasty did not have a class of nobility or aristocracy, but instead a class of scholar officials arose. In practice, government offices were monopolized by the scholar official class, as only this class had the resources and wealth to finance the long and lengthy education required to pass the civil service examinations. There was no more social mobility than in Greece or Rome - you were either born into a family with means or you were not. Even a basic education to attain rudimentary level of literacy was not within the means for over 95% of the population. Despite the imperial examination system, high government offices and wealth would, over the course of the dynasty, be concentrated in the hands of only a few dozen families.
Ultimately, the dynasties that adopted the civil examination system (Tang - Ming) did not last any longer than the Han. At the beginning of the dynasty, when wealth/land had been redistributed and power centralized, you had a relatively large degree of social mobility and meritocratic rule. However, over the course of generations, wealth and power would be monopolized by a small number of families, social mobility becomes impossible, the livelihoods of the common people suffers, and the state becomes weak and ineffectual.