Is a king truly a king without people to rule over?
These nobles are all trash. They think the commoners would be nothing without them... Yet they are no better than leeches who suck up the blood and tears of the actual working people. Nobles were never needed. People have managed to survive without them. But nobles cannot exist without commoners to take from.
Nobility is not inherently evil. Basically a noble lord is a governor.
As a governor needs to be competent and well educated, it's best to train someone specifically to be a governor, especially in a time where every hand was needed and higher education required too much time.
To get the most competent and educated governor possible, you train the future governor from childhood.
To do this, you need to have a family that is willing to give their child to the governor's estate for full time education, and the family most likely to do that is of course the governor's family, as they can still stay together with their child.
In conclusion, until the development of a dedicated middle class, nobility was by far the most effective form of government on paper. Only after the development of a middle class were commoners capable of getting higher education, as they had less tasks to do.