I assume the answer will vary wildly depending on the time period and region so lets say we are talking about 1100's England.
It was absolutely much more fluid. There were hierarchies in a way, but not rigid one, they were ever changing and multifaceted. As for your question, there were no counts, dukes or emperors in 12th century Britain. There was a king, bishops, and barons. There were also a relatively small amount of Earls, a title somewhat equivalent to count but not the same. So basically the way later medieval English political society worked was the king would delegate a local nobleman, usually a baron, with an office -- sheriff, justice of the peace, warden of the Scottish marches, castellan of a castle, etc. This person would exercise their office for the king, but use and build a personal power network -- affinity -- out of other barons and the gentry (lowest and most numerous part of the aristocracy who held small amounts of land and no title). An earl or baron did not hold a county as a vassal but instead influence a region as an office holder exercising royal power. The royal courts technically encompassed the entire kingdom, noblemen simply "influenced" the proceedings. Manorial courts or courts in private hundreds did exist, but did not have large jurisdictions. Furthermore, these networks were mutually reinforcing and the gentry benefitted as well, they did not simply take orders from above.
It is important to note that title such as lord -- Lord Neville, Lord Latimer, Lord Hastings, etc. -- were not regularized until the 14th-15th century. Before that, there was no clear line between a baron and a knight/gentleman. The composition of the baronage changed often, it was simply clear at the time who was and wasn't a baron, for instance in the magna carta. The first Dukedom -- and a number of Earldoms -- were created by Edward III in 1337 to revive the peerage since at that time the number of Earls had dwindled. Also, keep in mind that being created Earl of xx did not mean you actually controlled that shire/county, it was just a title. So, for instance, the Earl of Warwick did dominate Warwickshire, but not because he was earl of Warwick, but because he controlled territory in the shire and was also the hereditary sheriff. On the other hand, the earls of Oxford actually had the core of their lands in Essex. The only exception to this rule is the Earls/Dukes of Lancaster, who were in fact given control of the County Palatine of Lancaster. This is not a major issue however as they were royal princes and always close to the crown, and the Duchy of Lancaster then merged into the crown in 1399 when Henry IV seized the throne (it still technically exists as a separate holding).
Sources:
I've read countless other pertinent works bust as the mods can be incredibly neurotic about claims being backed up I thought I'd site these specifically, happy to provide others if asked.
In fairness to the game, Dukes within one country are rather often more powerful than Kings of a different country. It's mostly the representations of within-country hierarchy that are rigid.
Also these English earls mentioned above were created after the Norman conquest , with the civil wars of Edward II's reign and several natural extinctions diminished by their numbers.