I'm not sure that Emperor Jagangs Sorcerors would agree with you ...
The Empire seems to instill a lack of compassion for the weak, as well as a right to rule by birth (how good you are) ... this doesn't mean a noble lineage, per se, but outright genetic discrimination based upon empirical evidence of utility.
Emperor Jagang: the dreamwalker, recieves much of his powers by birth, as do the sorcerors and other various magic users that work for him.
Meanwhile, everyone else is equal. Yes, that is the whole reason why I cannot see the Empire as being free-trade or social mobility (Capitalist, political/social Darwinism) because the Empire is outright genetic Darwinism. There are those born for greatness, and the rest are obligated to be dutiful servants without any aspirations or social mobility.
I suppose the main difference between Jagang's Imperial Order and the "Empires" is that after Jagang has taken over the world, he wishes to rid the world of all magic (ubermensch), thus becoming the only Exceptional person in existence.
Whereas the empires would continue to uplift those born exceptionally gifted. This is to say that there is no Social Mobility in the empire. At all. Even those exceptionally born are limited to only the role they are naturally good at. There is no room for aspiration to do other things, or climb the ladder of ranks. Ranks are determined as soon as you are born. Under a capitalist society of any kind, there is always some form of social mobility. Even in a fascist society (corporations ruling with the iron fist of the military) there is some social mobility, especially if the particular fascist society has no racial prejudices (very possible within the definition of Fascism).
A good example (Of Empires) would be the movie GATTACA
The Empires, however, would be most closely associated with Either Stalinism or some Stark retelling of Chinese Imperialism. (meaning all the Chinese politics and none of the Culture). In both cases, the only people elevated above the level of Peon are the Bureaucratic Administrators. These people would be selected by Nation-wide standardized testing, and being selected for their naturally high intelligence, the logic would dictate that they would be the best to control the central authority of the government.
A highly simplified version, I am sure, but nevertheless a useful Foil.
Meanwhile, the "Kingdoms" seem, to me, most like the city states of Ancient Greece ... with elements of republics, excess of extreme democracy, and other elements of complete authoritarianism. In these societies, decadence (Culture) is allowed and often encouraged, while politics are often placed within the hands of the people. Social mobility is often acceptable, through proving your worth to your fellow men to be elected as a Senator or Administrator. In this society, the key emphasis is on self expression ... and by extension you get to pick your own rulers. The only difference with the Kingdoms, of course, is that the Sovereign actually has all of the power and could take away any civil freedoms he or so chooses at any time.
In this way, the Kingdoms are even MORE like the midlands ... because they have a system of Absolute Rule (Lord Rahl, Mother Confessor) while at the same time the people are encouraged to pursue self expression (many tolerated minorities, magics allowed in all forms, social mobility).
Sparta would actually be closer to an Empire due to their Stark and Spartan nature, with selecting the role of a child soon after birth, sacrificing of those physically handicapped, etc.
Thus, as you can see, the Imperial Order does hold many similarities with the Empires and the Midlands hold many similarities with the Kingdoms.
Elemental Forums
I'm almost a quarter into A Game of Thrones as we speak.