the big thing is what do folks consider self taught? When someone says they were self taught, why do people act as if they just sat in front of the instrument isolated and figured out EVERYTHING with no assistance whatsoever? These folks learned from other people as well, probably a LOT more in the earlier stages than maybe say now, but they did learn from others. Whether it be from books, videos, forums like this, youtube, watching others play, listening to music, etc. they learned from others. It was just a solo effort in getting this information gathered together and utilizing it.
I bet any of them would say, if you had the opportunity to have a teacher or go to school, to take that opportunity. Knowing how things were for them and sometimes wishing they had those resources or someone in the know to ask at ANY time ANY question, they would say jump on that. Some of them even do teaching themselves. Why do you think they post videos and be part of workshops and stuff. Otherwise anyone that asks them something they would say "get away from me and go figure it out on your own". None would try to give tips or correct bad habits but rather say "he'll figure out in a few years that he's doing it wrong or that theres a better way". Take note that many were self taught as an only option, not because they shunned any other way to learn (school or personal teacher) or thought it was pointless or stupid. Most had no options.
T-Block and Tip said it. Having that proficiency over your instrument, and a level of mastery over music in general will help you play anything. If you can do some of that classical stuff, which takes crazy skill, you telling me u cant do a gospel shout run??? If anything, now you have even MORE stuff to throw in there, and because its not the normal gospel stuff that everybody else do, its out of the box and a head-turner. What you think these other guys do? They study other genres of music to open their musical palate. For many, going to school for music does that from day 1.
My first music teacher had a jazz background. My second bass teacher was all R&B. Third teacher all funk. Way different styles, different tips and suggestions on how to play, different materials of music to listen to and learn, different emphasis on certain techniques and patterns. First teacher focused on theory, could read sheet music had me playing in concerts from chord charts and practicing off sheet music. Third teacher has no theory but good ear so he works my ear to learn songs. Second teacher was a balance of both. Both bass teachers played with my other music teacher back in the day. NONE of them taught me gospel songs, but yet I play in church every sunday.
Also, remember that when you become a John P Kee or a Richard Smallwood (the performer/artist) your focus isnt really the same anymore as someone who is only known as a musician (and only by other musicians). Its hard to put that level into the craft (and exploring new dimensions of it) while doing all the other stuff. Same deal with Kirk Franklin and Fred Hammond. But who's to say that the classical training isnt what helped them become those household names in the first place.