It seems to me that you’re attempting to equate an internal monologue with intelligence, and I don’t think that’s a fair assumption. An internal monologue is just a brains way of formatting its thoughts and feelings about the information that flows in. There are many ways to do this, and one way isn’t necessarily “superior” to another. That’s just how brains work. And while many intelligent people do have this internal monologue, it’s absolutely not necessary for intelligence.

Side note, one of the most brilliant people I’ve ever met is aphasiac, and doesn’t have an internal monologue.