Well "soul" can have different connotations in this discussion. There is "Soul" as a descriptor of certain forms of music. But there is "soul" as in whether something has depth and isn't superficial.
I think there's a number of ways in which the word 'soul' gets used. Obviously, it is the name for a particular genre of music 'soul'. However, as a musician I've noticed that there is usage of the word which brings up a stereotype regarding (so called) 'black' vs 'white' music.
The stereotype is essentially that 'black' popular music culture is cooler, hipper, looser and has more emotional heft (soul) than 'white' music which is restrained, uptight and less expressive (not soul). As such, there's plenty of Caucasian musicians who believe they play or aspire to sound what they think of as 'black'.
Check out the movie 'Crossroads' (with Ralph Macchio, not Britney). Young white kid at Julliard playing classical guitar but obsesses over country blues music in his spare time. He tracks down the legendary 'Willie Brown' and busts him out of a nursing home to go on a journey down south into the delta to learn the secrets of Robert Johnson and his 'lost song'. The whole movie is about Ralph Macchio struggling to gain musical & cultural acceptance from African Americans. "See? Look how cool I play...I'm just like you, please love and validate me!"
The movie has a supernatural twist. Willie Brown sold his soul to the devil at the crossroads in exchange for his 15 minutes of fame in the world of blues music. Ralphie steps up to the challenge to win back the contract by battling Steve Vai in a head-cutting guitar jam contest.
Ralph plays bluesy bottleneck slide riffs (played by Arlen Roth) while Steve Vai was basically being himself. Well, lo and behold Vai comes up with a lick so brain melting, Ralph's confidence is shaken - he might not win! ERHMAHGERD! And what does he do? Why, he puts down his glass guitar slide and hammers out a classical piece which had some Paganini runs in it. Vai in his role of 'Jack Butler' cannot copy the lick and thus Faustian pact annulled, Willie saved and devil unhappy but, a deal's a deal, right?
So for 99% of the movie, Ralph Macchio wants to be the ultimate blues man, until his ass gets in trouble when he meets the shred monster so he plays [ahem] so called 'difficult, proper music' and wins. [It's stupid...not as stupid as that movie 'Soul Man' about the kid who sports black face to get into college. Of course, none of the real African Americans notice..wtf...]
Contrary to the stereotype we have Wynton Marsalis who plays classical music. Jimi Hendrix idolized Bob Dylan, Charlie Parker wanted to hang with Stravinsky & Miles Davis did some of his best work with Gil Evans (who was white and Canadian
). And then there's dear old Elvis who popularized 'Hound Dog', a cover of a song originally done by Big Mamma Thornton but was written by Lieber & Stoller who were Jewish. Jazz musicians love playing songs by Cole Porter who was white and gay and also works by Billy Strayhorn who was black and gay.
The reality shows a great deal of complexity and diversity. However, there's still an idea in pop culture which equates ethnicity to authenticity. It's a bullshit idea but it's there. It's why people are like "Wow...can you believe Eminem raps so well..and he's WHITE!???" One of my (black) friends (lol, love a cliche) thinks the sun rises and sets on Coldplay. Some of his other (white) friends thinks that makes him less African-American.