I think these terms, king, queen, empress, godfather etc are rather pointless.
Of all the artists mentioned, I think JB was the one that did the most for his people. In the aftermath of the MLK assassination, Watts, Chicago, Detroit etc, it was JB's voice that people listened to and held the most sway in the community. In creative terms, the man was unique, an total innovator. If the JB groove and what became Funk isn't one's cup of tea, it hardly matters, the man was a pathfinder. As a performer, the man was also in a class of his own. If we go back further in time, ask yourself these questions: if Bessie Smith was the empress of the blues, wtf were Ma Rainey and Victoria Spivey? Was Robert Johnson really the king of the Delta Blues?