Ian's undergrad degree is in Rhetoric. In other words, he's been trained to use the language to his advantage to win debates, inflate the value of his points and devalue yours.
There's nothing inherently wrong with rhetoric. The word has taken on a negative connotation because it's been associated so often with things like "political rhetoric," where rhetoric is all about "taking advantage," "inflating value," "devaluing the opposition," etc. But true rhetoric is a much fairer, much less negative enterprise, and I happen to think you're too quick to brush Ian's approach with the negative connotation of rhetoric.
He has always said he wants his time with a guest to be a conversation. That's a distinctly different style than Knapp, coming from an investigative journalism background. Knapp does what journalists do--asks questions and stays in the background, out of the way, while the guest expounds. Ian's style seems more or less a dialectic.
Personally, I don't find one style superior to the other, merely different, and enjoy both these hosts for what they do and how they do it. But that's just me.