Hi Azizi - Greetings from Down Under!
By no means do I know a lot about traditional Australian Aboriginal music but ....
it's made solely by voice and didjeridu (latter only in a few regions), and percussion (hand claps, tapping boomerangs, pod shakers) ...... however, syncopation & off-beat emphasis don't seem to be a factor.

Shall add the John Storm Roberts book to the wish list (I already have the other two - thanks)
And let me recommend my very favourite music writer (who happens to have written what I consider the Gospel Music 'Bible") - Anthony Heilbut, author of "The Gospel Sound" (Limelight, NY, 1997, 25th anniversary edition)

GMWA = Gospel Music Workshop of America.
It's the huge (largest?) long running (founded by Rev James Cleveland late '60s) annual Black music convention, different cities most years.
Btw, if you visit my website - just Google my name - you'll find pics of myself there with my favourite Gospel singer, Albertina Walker, and Billy Preston (brother of the massed choirs director, Rodena Williams).

That Langston Hughes script for BLACK NATIVITY remains the same, but I gather the annual updates mean the show's songs and presentation have changed mightily over the decades .... I'm still hoping to track down the (European, I think) B&W TV show of the original cast, which included Alex Bradford & Marion Williams .....

Cheers
Margret