He was not overlooked, he was a catalyst. Blues was bigger in the 80's. After Vaughan's passing, the blues crossover that was on commercial radio went on the decline. The torch was not passed. Robert Cray was the best hope for the future at the time, but he has faded. There is no new blues stars that get airplay on mainstream radio.
Somewhere between Robert Johnson and Steve Vai. Okay, that was a loaded answer. I agree with you, but I think that here in the 'stratosphere', there is no real way to quantify and rank talent on his scale. It mainly boils down to opinion and personal taste. Most definitely at or near the top...in my opinion, hehe.
I don't really care for rating musicians, but I certainly consider him one of the greats. I don't think his playing is overlooked at all, but maybe his singing. Listen to Ain't Gone N Give Up On Love with headphones and you'll see what I mean.