I concur, however:
There was more than one kind of feudal state, and each was different more than just a title.
Frontier Vassal: A state set up as an effective buffer zone between the mother country, the center of civilization, or whatever. Effectively a military frontier. The various marches (Scottish, Welsh marches, Brandenburg, Marche, etc) were all set up to be more effective military machines than ordinary counties, and the ruler was granted special powers in order to defend the frontier that other counties were barred from possessing (the king kept that authority for himself).
Has almost the same level of state control as a king, but not the prestige. Ruler titles: Christians: Marquis, Moslems: Ghazi.
Vassal: A state set up to govern a territory on behalf of a king, with various limitations on the power and authority of the Count. The Count of a County has very little power, and the cities, towns and local aristocrats can easily deflect his will. Christians: Count (in England: Earl, in Germany: Baron), Moslems: Sheikh
Tribal Vassal: A vassal created by a king, but ordered along ancient ethnic or regional lines for its authority. These tend to be more powerful within this ethnoregional area than an ordinary vassal state. Christian: Duke, Moslem: Bey.
Palatine Vassal: A county set up with special added prestige in order to offset other powerful vassals of the king. Christians: Count-Palatine, Moslems: Sharif
Royal Vassal: This Tribal Vassal is set above other dukes so that its authority is more akin to a king than a duke. Christians: Archduke, Moslems: Khedive
Viceroyal Vassal: This Administrative vassal is set above other govenors so that it's authority is more akin to a king than a govenor. Christians: Viceroy, Moslems: Pasha.
Administrative Vassal: This official is appointed by the king to his post, and is entirely dependant upon him for his authority. Christians: Govenor, Moslems: Wali.
Military Vassal: This vassal is an appointed military commander who rules his territory as a govenor. This is highly advantageous in terms of military strength but has long-term problems. Various names: Moslem: Sanjak-bey, Bulgarian, Czech, Polish, Russian, Lithuanian, Serbian & Romanian: Viovode, Croatian, Bosnian, Slovenian & Hungarian: Ban.
Despotic Monarchy: An independent state based on absolute power of the ruler and force of arms. Orthadox: Despot, others: Prince, Moslems: Emir
Sanctified Monarchy: The religious authorities have declared this ruler Gods Representative for secular matters (or even an actual god). Christian: Caesar, Moslems: Caliph, others: Divine Emperor
Tribal Monarchy: The monarch is the leader of a people (as in "The French" or "The Germans"), and his authority is derived therein. Most of the time this is a King, except Turkic peoples who are ruled by a Khan.
Absolute Monarchy: This monarch IS the state, the supreme and sole source of all authority. Christians, others: Emperor, Moslems: Sultan.