I found this one interesting: Escaping the Delta
The author peels away the layers of myth surrounding Robert Johnson. His take is that the blues were one genre in a mix of many, all influencing each other. He also takes issue with the concept of Robert Johnson being the father of all blues that followed him.
You need this book. It demolishes a few myths. And I speak as a blues fan.
In any case, "in a few years" is plenty of time to "master the guitar" to his level, especially if you start young, as he probably did. He was at least 10 years younger than the first generation of blues artists on record, and he had good mentors. Like this guy.
And FWIW, this guy was a better guitarist than Robert Johnson. That's 10 years before Johnson recorded.
Johnson was great, no mistake. But (beginning in the 1960s) a legend built up around him, for various reasons. (1) He died young, in mysterious circumstances. (2) He only recorded two sessions, around 40 tracks. (3) He had an unusual (for the times) introspective style, more tortured and melancholy than most 1920s/30s blues singers. (4) His guitar style (not that much better if at all than some of his contemporaries) was equally idiosyncratic. (5) He was fairly obscure in his lifetime. All these things made him stand out, as a character who - for white fans in the 1960s - seemed to represent everything they thought "the blues" was all about. Let's raise this poor guy to the throne he deserves!