Yes, I know they are separate, but they are both shadows of a class system that is repugnant to modern western values. And although what you are saying is true, it is only the current practice. Notice that the UK has no written constitution.
It particularly astonishes me when Americans defend these costumes, given that their country was essentially created in opposition to such a class system.
Pretty much everything that happens in the present is the shadow of some or other repugnant historical practice or event. Knighthoods are just one of the civilian honors you can get in the UK. It's not much different from the Presidential Medal of Freedom or something like that. The honor happens to come with a title. There are similar perks in US culture (e.g. Professor so-and-so, Doctor so-and-so).
Knighthoods (“Sir”) are in reality awarded by decisions of the elected government, though nominally by the Queen.