The right to petition the Government for redress of grievances is included by our founders for a reason - because it was NOT a recognized right under feudalism.
Your idea that “true” separation of powers is a Baron saying “King - your son is out raping peasant women - please put a stop to it.” is truly delusional bootlicker.
I recommend, for starters, Morris Bishop. The Middle Ages. ISBN 0-618-05703-X.
Feudalism was a set of legal and military customs in medieval Europe that flourished between the ninth and fifteenth centuries, which, broadly defined, was a system for ordering society around relationships derived from the holding of land in exchange for service or labour. Although derived from the Latin word feodum (fief),[1] then in use, the term feudalism and the system it describes were not conceived of as a formal political system by the people living in the Medieval Period. In its classic definition, by François-Louis Ganshof (1944),[2] feudalism describes a set of reciprocal legal and military obligations among the warrior nobility, revolving around the three key concepts of lords, vassals and fiefs. There is also a broader definition, as described by Marc Bloch (1939), that includes not only warrior nobility but the peasantry bonds of manorialism, sometimes referred to as a "feudal society".The lord held a manor court, governed by public law and local custom.
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Though not free, villeins were by no means in the same position as slaves: they enjoyed legal rights, subject to local custom, and had recourse to the law, subject to court charges which were an additional source of manorial income.
The American colonies had indeed a valid compaint; in fact my guess is that few monarchists today would take a loyalist position. You should not take their demand for redress of grievances as a prove that in the Middle Ages (the epoque I primarily am oriented toward) there was no concept of such. To the contrary, manorial court was the central governing organ in the local government. See Manor Court
Also note, please, that I substantiate my assertions by reference to material that is neutral in character.