What you're describing isn't self-taught vs. formally educated. It is curious vs complacent w/ a heavy sprinkle of hard work, creativity, and intelligence.
Both groups can have those traits. Self-taught can ONLY work well if you have those traits, so maybe you more obviously see it in that group since it's a requirement to succeed when self taught, whereas a classically trained engineer without those traits will probably still "make it". An engineer with those traits and the formal education will do better than either category most of the time.