As I said, he could have done better, and I don’t disagree with you on that.
But consider that he has purposely cultivated the image of a non-politician. If he came off with a slick answer to every question or challenge, it’d undercut that image. That’s a LOT of his support.
Maybe some middle ground between "slick answer" and incoherent rambling might be a good idea. And either way, letting Hillary completely off the hook is inexcusable. At this point, he is not courting his base - and if that support will be undercut by having competent answers then he is in deep trouble - but he needs to convince the "independents" and "undecideds" to vote for him instead of Hillary.