I do get your point about the blues residing in obscurity. But aren't you putting the cart before the horse? Would the blues exist absent racism, poverty, alienation, etc.? For what reason?
One issue I have with claims of appropriation is the implication that a style such as rythmn & blues derived from whole cloth. It didn't. It also had antecedants—hymns, spirituals, African music, synthezised into what came to be known as blues & jazz & ultimately rock & roll. After all, would songs such as "Crossroads" exist outside of Christian culture?
I'm not sure what point you want me to get exactly. You say the Stones aren't that great, that they've been vaulted to "mythical" status. I don't really follow. I don't think the Stones are mythic in the same way say The Beatles are, because the latter broke up, & stayed that way. They didn't age before our eyes, or continue to release albums of increasing mediocrity. We remember them as they were. Not the same for the Stones.
Yet I think you're saying you don't really care for them that much. That's fine. That's your perogative. But that doesn't make them poseurs. They'd be poseurs if they claimed to be playing authentic Delta Blues, which they don't. Being influenced by a style isn't the same as claiming to have mastered it.
I'm not a huge Stones fan myself, but I believe they created enough "value added" to their music to be regarded as authentically great, at least in their heyday.
If I understand you correctly, you seem to be saying we should be listening to Robert Johnson, or Muddy Waters, or Leadbelly & that's it. Music shouldn't move on, shouldn't develop, styles shouldn't change, or genres evolve? Are rappers also poseurs?
Finally I have to disagree re the Brits. Of course they have accents & slang unfamiliar to us. But I think you're forgetting that our laws are also based on English Common Law. In fact, if you really think we have as much in common with the French as we do the British, look closely at how French criminal & civil laws work ... most Americans would be find French criminal courts baffling. While we'd easily understand British courts.