Great observation, and I don't disagree.
But there is music theory
before Jimi Hendrix, and then there's music theory
after Jimi Hendrix. He changed the music theory textbooks. Maybe it was only a few inches, but he moved the ball forward.
Perhaps in order to be a pioneer in certain areas like Hendrix, there are other roads you don't get a chance to explore. Nobody is good at
everything. (Or at least, nobody has the
time to learn how to become good at everything, especially if you don't live to see your 28th birthday.) Stravinsky didn't write a lot of fugues, for example, but he certainly had an elite-level understanding of music theory.
Personally I think Hendrix's elite-tier music-theory genius (perhaps the word 'savant' applies?) was in the fields of
sonority and
orchestration. Many people have had the experience, upon hearing Hendrix for the first time, that they are listening to something other than a guitar, or hearing more than three musicians onstage, or experiencing a familiar song in a completely unexpected way (Star Spangled Banner), or even opening up vast cosmic mind-out-of-body new horizons.