And instead produced a new sort of Leto II, who this time had evolved to the point he could safely merge with and control not the worms but the machines, balanced out by new Leto II ghola merging back with the worms, creating Shai Hulud for real.

I think one of the general tangents pursued by Herbert was that the BG's program (and the Tleilaxu) was using Man and genetics to transform humanity into a race of "thinking machines". It had a machinistic view of Man, with precise characteristics and precise purposes it sought to obtain, and this would have ended evolution, and the human race as such, readying it for enslavement and annihilation when the Machines returned, and Leto II had foreseen their return. Man feared the thinking machines, but was turning into a flesh and blood version of them, and Leto planted the seed to prevent that, including giving them millenia of a machine-like stagnation and order in his Imperium. The Humans otherwise would succeed were the original thinking machines had failed with humanity. The HM were hard at work trying to control and program the fundamental forces like sexual desire that drove the survival of the species, which was crossing a line the BG of Paul's time had not.

Leto II's Golden Path, and the "wild genes" introduced into humanity, made it impossible to obtain predictable results from genetic programs, old school or gholas. Sheena, Idaho, Teg.. they escaped. The God Emperor gave humanity the "random" characteristics that would make them unpredictable to the machines.

Dune 7 confronted these "new humans" (and the gholas of the original cast) with their wild genes with the machine-like new Face Dancers and the remnants of the Machines of the Bulterian Jihad that now controlled them.

IMO, Herbert always intended to deceive us at the end of Chapterhouse into thinking Marty and Daniel were Face Dancers/their masters. I think the infernal duo was actually following Frank's outline by revealing those two as Machines disguised as the gods of the new Face Dancers. Most readers at the time disagreed with my opinion (and I suspect most do), but I base it largely on the similar themes and ideas Herbert was exploring in parallel in his series with Bill Ransom at the same time he was developping the last Dune trilogy.

I have no opinion, however, whether the two machine characters Daniel and Marty turn out to owe much to Frank's notes or had to be created pretty much from the ground up by the infernal duo after nothing but something as basic as "these two will be BJ machine minds - needs to be developped", though my guts tells me Erasmus is nothing but a very poor execution of a concept sketched by Frank... there's something at the core of the character of Erasmus which is too intelligent for him to be BH/KJA's concept... Erasmus is too much a variation on other AI created by Frank, like Ship, too intelligently merged with the Dune universe and Dune themes.. despite the fact the duo proved unable to really bring this character to life. The name itself speaks in favour of a creation by Frank, I think.). Generally speaking, through the narrative dross that's Dune 7, many of the ideas are too intelligent and too characteristic to be anything but Frank's, because the House and BJ prequels have shown how incapable the duo was at any thinking of this sort. I don't think a miracle happened and with Dune 7 the duo was suddenly capable of creating even some Frank-like concepts of their own. What I see is rather that despite their limited talent, they weren't able to completely strip the book of Frank's intelligence.... they just wrapped them in their dumbed-down stuff (it's nowhere as bad as their prequels, mind you).

There's this slim possibility the duo turned to steal the ideas in Franks's other books because they were quite incapable of introducing their own to fill the intellectual gaps, but I'm fairly confident it's more a case of attempting to flesh out the basic ideas set in an outline.

Where these ideas lost much of their interest, and much of their intelligence, is when the duo attempted to work them backward into their prequels. They've "tainted" Dune 7 with their back story.

I'm sort of convinced, for instance, that it's Frank who decided the conscience of the woman who invented space folding had moved to another plane of existence and was a kind of God to the Navigators and she would guide Idaho. That's a terribly Frank-like concept, very Fanny-May in The Whipping Star. This got ruined by the fact it wasn't introduced in Dune 7, where it fitted with the rest of the motifs of evolution spiritual and physical and the nature of religion and God, but a whole pedestrian, dumb and boring back story for Norma was written into the BJ prequels. A completely useless backstory for the Tleiaxu was also written that we didn't need to know in details, nor before Dune 7. Erasmus also got ruined by his back story during the BJ. If Frank has created the concept of the Titans (I'm not so sure), this is yet something else we didn't need to know about until Dune 7, and we most definitely didn't need to see them in action in BJ prequels where the perhaps cool concept was turned into ridiculous Transformer-like cyborgs.

Where I think the duo failed the most in Dune 7 is in their use of the "original cast" gholas. It's very obvious in Dune 6 Frank was going there in the next book, but it's one area in which I think probable his outline didn't give much, or at least it turned into one of the definitely weaker aspects of the "duology". Another is the continuation of the Murbella story line. The action-oriented/episodic nature of the books is also very much to blame on the infernal duo as well, based on their previous Dune books.

But overall, these ideas of super-worms, ubermensch, mutations, the nature of God, and the perhaps most of all this idea that humans yearning for God may have ended up creating a false God that enslaved them are IMO terribly Herbert-like. These are all variations on themes, other aspects of themes, he was exploring with Bill Ransom in the Jesus Incident/Lazarus Effect/Ascension Factor.