Generally speaking, it's very much worth emphasising that black American music is very much an American music.

Broadly speaking, the musical features of black American music was not studied in detail in the antebellum era, and our sources for understanding that music at the time are largely through things like (kind of clueless) references to the music in the memoirs of white people who spent time on plantations (and the like). And inevitably, white slavers in America did not remotely care about the specific African cultures of the people they enslaved, and enslaved people were as likely as not to end up working next to people with very different cultural traditions. Additionally, Africa's music does not stay unchanged; you can't simply compare features of the Mississippi Delta Blues to the music of a particular African culture in 2018 and assume that the music of 2018 in a modern West African country reflects the music of 1755. As such, we shouldn't expect features of black American music to necessarily have a specific origin in a specific West African culture; in fact, often the distinctive features of the music that have survived are the ones that different people from different backgrounds in different parts of West Africa shared in common, and which could therefore be a common ground (e.g., the use of melisma in black African music has been traced back to Islamic singing styles which in the 7th and 8th centuries became common around North Africa, and then slowly dispersed their way through other parts of Africa, such as West Africa.)

Mississippi Delta Blues, for example, is often seen as an example of an unusually 'primitive' (and I very deliberately put that in inverted commas) or particularly African-influenced music. But the Mississippi Delta Blues has strong cultural influences from European music. Most obviously, it's played on European-designed instruments, and by people who grew up in a European-dominated country, and thus there is much about its tonality and rhythm which is distinctively European-based. The 'blue note' is a good example of that, because the 'blue note' - the tendency to slide between the minor and major third - is a compromise between African roots and European instruments. The blue note sound developed a meaning of its own in American music, based on that compromise, which is separate to the meaning of similar notes in West African cultures. This goes for ragtime as well; for starters, ragtime is very much associated with the piano, an instrument that is the most obvious examplar of European tonality.

Additionally, the blues musicians of the 1920s and 1930s who made the first blues recordings - and thus are our best windows into what African American music sounded like way back when - were not primitives. They were very often working musicians who could play many styles, and if they sound like their music is quite primitive, it's often because they were encouraged by white producers to make music they thought would sell, focusing on particular parts of their repertoire. So they did not simply grow up in one (black) musical culture with begrudging reference to another (white, English-speaking) one. And blues music has obvious influences from Spanish musical dance forms such as the fandango, and in the way that blues musicians not only used the guitar as their dominant instrument - there's a reason why playing guitar in the usual fashion you see the likes of Ed Sheeran playing it is called 'Spanish style'. There was also a clear influence from Spanish guitar music on the way that blues musicians used 'open tuning' on their Spanish-style guitar - how exactly this influence developed is a bit of a mystery, but it is clearly there. Similarly, one of the distinctive parts of the Mississippi delta blues as recorded in the 1920s and 1930s is the use of slides on the guitar. People have found roots of this in Africa...but the blues musician Son House, however, who recorded in that era and was still around in the 1950s/60s when people started paying fevered attention to that music, attributed his interest in slide guitar to a craze in that era for Hawaiian music.

So, all in all, the answer to your question is no. We are impoverished in our understanding of black American music's origins, by our inability to hear the past in an era before recordings. We are also enriched by the ability of black American musicians to take a wide array of influences and ideas and create new musics which reflected their circumstances.