The Tristano story brings to mind a Bill Evans quote "I study the minimum of material but very thoroughly". Obviously to be a working jazz musician (or any kind of popular music) you need at least a passing familiarity with a whole lot of tunes. But it's also true that you simply can't do a deep dive into every single tune in the canon of whatever you're playing, be it Dixieland, western swing, punk, or what have you. The human brain, however, if left alone and not constantly distracted with "ooh, new shiny!" is exceptionally good at drawing parallels from one thing studied thoroughly, to other related things. So if you do the deep deep deep dive into "scrapple from the apple", what you learn there will TRANSFER OVER to other tunes, far more than you might think.
I suppose it may be possible to do on-line learning for the deep deep dive stuff. But I don't think there's any way online can duplicate the actual rubber-meets-the-road environment of playing African American improvised music with other people for an audience. It's real time composition.
Or, to put it another way, you can ABSOLUTELY learn to play convincing, compelling jazz (or other varieties of AA improvised music), with minimal theoretical knowledge and formal instruction (whether in person or on line), and maximal personal experience on the actual bandstand. You CANNOT learn to play convincing, compelling jazz (or other varieties of AA improvised music), no matter how many theoretical lessons you learn, WITHOUT direct personal experience on the actual bandstand.