jb,
Welcome to the Mudcat. As you can see, no one will answer your question definitively, because there is no definitive answer.
We've had this question asked before in other ways, and the answers are always the same.
So, you get opinions, and I'm not shy about adding mine. For some blues has been a way of life. For others it has been a way they feel. For others it has been a musical style. But it's all blues.
Somedays on some songs Eric is a blues singer, other times he is pop singer. Somedays on some songs Lead Belly was a blues singer, other times he was a children's artist.
I guess I'm saying it ain't the singer, it is the song and the particular performance.
In the end, we don't need the label except to classify our CD collections. Labels by necessity become exclusive. I prefer to be inclusive, so it's blues if you say it is blues. It doesn't mean I'll like it.
Roger in Baltimore