I dont dissagree on any particular point, and accept some corrections, but I suppose its a question of perspective, and its all relative.
The perspective, to me, is on the variation within blues and the amount that it can and does change/has changed both as a whole and if you take any given blues artists carreer, and compare that to one of the other major Churches of Guitar, like metal, rock, jazz etc.
I find it wanting in that regard. Certainly it *did* change, but how much? Compare Mayer to SRV; very, very similar to my ears. Maybe I'm missing something magical and ethereal (but, y'know what, maybe thats not there, maybe its hype, or beauty in the ear of the listener or whatever, but, carrying on) but they sound really similar to me.
Now compare, say, black sabbath with nile. OK, the latter is faster and heavier and whatever, thats not the point, its also far more catholic and far more sophisticated music. It has a clear mission statement (be $%ing heavy, same as sabbath) but is far more free within and around that mission, and includes from MANY other forms of music while still retaining its The Metal identity.
Or even one artist and another form of music: jazz and lenny breau, similar thing; he evolved and changed and experimented, and he didnt at any point sound like, say, joe pass or wes montgomery, who did much the same. These guys all also played music with much the same sort of genre identity, but diversified it and included in it from many other things.
Its the lack of variability that gets me. Its there, its just (relatively) tiny, and I dont understand why the genre is so constrained compared to other forms of guitar music, which are have all diversified and intermingled massively over the years.
Which isnt to say that the blues hasnt spread into other things, it just seems like there have been people trying to play some pure-bred Platonic Form of the blues for decades now, and it doesnt change or let anything else in.