Perhaps you misunderstand me but I'm not bashing Brian Herbert and Kevin Anderson. I enjoyed their House Series and would like to finish Paul of Dune and Winds of Dune eventually. However the further they got away from the main Dune storyline of the first three books the less interested I became. Granted it was the same for Frank Herbert's later Dune works as well.
I disagree with you about not comparing them to the Frank Herbert novels though. Especially the House Series which is a prequel to Dune and the Paul and Wind books which are in betweens for Messiah and Children (I believe). The books were only written because of Frank Herbert's previous novels and part of their appeal is shedding more light on the characters and events leading up to or occurring during or around the stuff that happened in Frank Herbert's books.
Actually, I was speaking generally. Brian Herbert and KJA's books are usually universally panned by fans, which I think is unfair since they are mostly half decent books. True they might not be in the same league as Frank Herbert's, but they're decent reads all the same.
And I happen to agree with your assessment of them. The House trilogy is pretty decent, the Jihad trilogy not so much. The Hunters of Dune/Sandworms of Dune duology is pretty good even if Sandworms has a certain revelation which I understand doesn't sit well among fans. I even enjoy Paul of Dune, Winds of Dune and Sisterhood of Dune even if they maybe prequels too far.