The HRE had no unifying culture or language, just like the FWL. Of course there were clusters (west of the Rhine, south of the Alps, along the shores of the baltic sea, central germany) of shared language, but for the whole state there was a lingua franca, mostly reserved for educated circles, with little meaning in everyday life.
The greek city states had a unifying culture and a language, while the Byzantine Empire had a common governance and (later on) a common religion.
The individual states making up the HRE are found in the FWL as well. That each had its own way to be run, with some feudal states, trade republics and theocracies is likewise echoed in the Free Worlds where plutocratic corporation regimes and basic sowjet-style democracies stand side by side with parliamentarism and aristocratic republics and everything in between.
The dynamic of how the individual states take part in the greater wars and are expected provide contigents of troops to travel with the Emperor/Captain-General (and frequently argue of how big that contigent has to be) is almost the exact same.
The FWL Parliament finds its counterpart in the Imperial Diet, especially the Permanent Diet.
The dynastic struggles (3014-15 and becoming especially prevalent in post 3067) in which noble families struggle for the right to fill the Captain-Generalcy are a strong connection too.
I don´t say your comparisons are wrong. There are elements of both, the greek city states as well as of the Byzantine Empire in the FWL. I just think the HRE shares a greater number of characteristics with the FWL. In the end it is probably a matter of where you put the emphasis.
Edited by Molossian Dog, 01 February 2014 - 08:57 PM.