MBTI (and/or Jung?) is kind of vague and a lot of people have different ideas about it. But the Jungian stuff equated introversion with turning inward or inside oneself and finding a kind of meaning or value in things, things that are almost always debatable to some degree. Extroversion, by comparison, turns outward and is much more focused on and defined by the external world, so it's usually verifiable in some way, but can also be very malleable.
I think it would be hard to introspect, without knowing what's valued or meaningful and why - the subjective experience or qualia. A problem perhaps for extroverts. But on the same token, without enough external input or experience, meaning and value that was once found may not align or mesh well with the surrounding world. And this would be a problem for introverts. I think introverts have a lot more problems sorting out how they see themselves and the world with how it actually is and will struggle with new experiences more, while extroverts have a harder time figuring out how they see things and what's important to them and why.
Maybe it's best to say that both are necessary to have a stable self-concept. But I do think this makes introverts naturally 'geared' towards introspection, even if the product of their introspection is not always or even very often represented well by the world around them.
