This is an either/or fallacy. To be excellent, you need a mix of both. Formal schooling isn't required, but you generally need to have been exposed to other smart people, many more experienced, because otherwise it's impossible to tell what self-study will be fruitful and what not. So some form of instruction, whether it comes from school or from a lucky landing in the work world, is required. That said, if you're not autodidactic to some extent, you're going to be unable to grow.
By the way, I've learned a lot of those "skills that self-taught people lack" on my own. Lambda calculus and type theory I hadn't even studied till I was 24. I'm not an expert on either, but I know as much as a well-educated non-expert (i.e. I know what the typed lambda calculus is and why it's interesting, I know about System F as the basis for ML, et cetera).
By the way, I've learned a lot of those "skills that self-taught people lack" on my own. Lambda calculus and type theory I hadn't even studied till I was 24. I'm not an expert on either, but I know as much as a well-educated non-expert (i.e. I know what the typed lambda calculus is and why it's interesting, I know about System F as the basis for ML, et cetera).