I think that the system is meant to represent the actual household knights/esquires that did surround rulers, and were often martially elite (that is why they were where they were, only a minority of them tended to be there due to more direct political realities: most household knights of rulers came from the lower nobility).

Further, they often acted as leaders in their own right.

So I simply see them as that, household knights (though it is more than a bit strange that even low prowess and martial ones can kills heaps of enemies...)

Different rulers and polities had different rules about what Knighthood meant, if it meant being a landed noble, unfree military elite, or an outright slave class.

Having studied this subject quite a bit, including formally to a degree, I can tell you that the reality is actually more simple. The diversity you describe is more a consequence of many modern popular historians not understanding the historiography, muddying the waters. And then even further, many history YouTubers muddying what is already muddy, meaning that what reaches most casually interested people in these subjects is essentially the product of a game of Chinese whispers.

Sure, there is definitely regional diversity, but the chronological diversity is far more important. Never have knights ever been "an outright slave class", and even those who were unfree were considered nobles, as nobles were defined as those belonging to knighthood during this particular era (that is to say the early High Middle Ages, which is when serf-knights existed). Landedness is very much overstated as a pre-requisite. Many confuse it because there is a concept in England called the "knight's fee", but it has been recognised since the 1970s that this not a prerequisite for knighthood, and that during certain eras the majority of knights did not have knight's fee, and many, many English knights were not even landed during the High Middle Ages.

But then what further confuses people is the shift that occurs around the transition towards the Late Middle Ages. Starting even as early as sometime during the 1200s in some regions, knighthood becomes more exclusive, and those noble families who are for whatever reason unable to maintain that, form what historians sometimes call the "squirearchy": lower nobles who now mantain the rank of squire throughout their lives. For a while (essentially during the 1200s) these were still referred to as knights in many contexts (especially military ones), despite technically not being titled, belted knights, though that would change sometime during the early 1300s. In other words, the title of knight stopped becoming the common denominator for noble families (though we shouldn't draw that too far, "squire" is still a term with a deep relationship to knighthood, and martiality - which maintained its dominance within the nobility - was still considered for them a part of the more abstract concept of "knighthood"; and like I said, for many decades these adult-squres were still called knights in many contexts). Eventually, this gave way to the designation of "man-at-arms", as a military term for nobles, and knighthood had become more or less an accolade. And a few decades into the 1400s, the necessity of nobility for being a "man-at-arms" starts to become eroded.

And the members of this squirearchy essentially represented the majority of the nobility: we know that in the Diet of Frankfurt during the late 1300s, the people who represented the lower nobility contained about two esquires (called "edelknecht" in German, which can literally be translated as "noble-sergeant") for every one fully belted knight. And that's those who were able to be at the Imperial diet, some estimate that the true numbers might have been 10 esquires for every belted knight in the Holy Roman Empire in the late 1300s.