Introspection is basically THE core mechanism for learning. That's HOW one learns on any topic. It's not a "wishy washy hippie feeling" (being provocative here) but rather introspection is (and to be fair I verified with https://plato.stanford.edu/entries/introspection/ just to make sure I wasn't talking out of my own ass) precisely looking at your inner workings. How you function IN ORDER to do better. You notice flaws, inefficient behaviors, things you enjoy, etc THEN you act on it.
Having no introspection is like doing math without verifying. It's like coding without compiling, linting or even executing without looking at the output.
So dumb it hurts.
By the way, his notion that introspection is an "invention of the 1920s" is historical bullshit. I think he's taking potshots at psychotherapy? Whatever, man, but then do that. It's not like a Freudian concept of the self is beyond criticism - far, far from it - but using that to interdict "introspection" is just sloppy thinking.
Anyway, leaving aside anything else to be said on the topic, the idea that "great men of history don't introspect" is utter bullshit. I'll see you Abraham Lincoln, and raise you Marcus fucking Aurelius.
So, if what you really want to say is that "most 'great men of history' were sociopaths" then, well, yeah: you're probably onto something. If your next thought is "and I want to be like them", then that's 1) a pretty damning confession, and 2) also evidence that you, sir, aren't actually a sociopathic "great man" at all, just an insecure nerd who got lucky a few times, and now are getting high on your own farts.