What you are missing there is something I stated earlier: These programs all advanced each other to one degree or another.
This is simply not the case to any significant extent. What you are missing is that there were generally multiple parallel lines of development in any given area that often did not influence each other very much. You cite inertial navigation; well, as I mention below, that was hardly something only North American was working on for their Navaho project. The same with rockets; you had the Army, the Air Force, the Navy, and NACA all working on rockets of various sizes. The same with reentry bodies; NACA, the Air Force, and the Army were all studying them. And, generally, they ended up coming to the same solutions about the same time; for instance, the Army (that is, Huntsville) and the Air Force (via General Electric) both independently figured out ablation during the development of their ballistic missile projects (the Army in 1955, the Air Force in 1957). Knock out one pole, and the others will just keep going as they did historically.
In science, it's usually the case that if you look at things closely enough, there was no discovery novel enough that it wasn't discovered twice, that is by two (or more) different people quite independently. The same thing is frequently the case in engineering, and it was certainly the case in the 1940s and 1950s.
With the Navajo program the inertial navigation system for that missile became the N6 system used on nuclear submarines and many other systems for accurate navigation in an era before GPS. Without it Polaris wouldn't have worked.
And there was a very considerable amount of work being done on inertial navigation regardless and outside of the Navaho program, given that it has obvious utilities for bombers, submarines, ships, etc. For instance, Charles Stark Draper was researching inertial guidance completely independently of the Navaho work in the 1940s, and this work was crucial in having Atlas go forwards in 1955. Not having the Navaho program would just mean that Polaris would use a system with a different heritage, not that it would just collapse in failure.
Jupiter and Thor both used engines developed from the G-26 and G-38 rocket booster engines for Navajo.
And Jupiter and Thor were both terribly useless militarily, given their long fueling cycles and short ranges. At least Atlas and Titan had the excuse that there weren't that many Soviet ballistic missiles around, and they were very inaccurate. If anything, the G-26 and G-38 were tremendous wastes of money, developed at great expense for very little to no military utility. It would have been far better to pour that money into advancing the state of the art in solid and hypergolic engines, so far as the military was concerned.
And, again, this whole thread has been about the ballistic missile program, not the cruise missile program. You keep bringing up the Navajo and Snark and similar programs and I'm not sure why, because no one except you is talking about them.
So, what you have is these programs feeding off each other to advance to completion. You limit it to one or a few and many of the advances vanish or would have taken much longer to occur. You need more than an engine to make an ICBM work.
No, if you get rid of the ICCMs and limit the number of programs around, what will happen is that the advances made for the ICCMs will be made for other programs, like the long-range bombers (for whom similar problems apply, anyways) or the ballistic missile program. I say this because this was in fact what happened--the advances needed to make the ballistic missiles work, the fundamental ones, took place before the programs started, for other purposes, and enabled the programs to begin in the first place.
Moreover, I'm not sure why you posted this as a response to me, because it has literally nothing to do with what I said. What I said was: the intercontinental cruise missiles started development before ICBMs (true). They were having serious technical difficulties by the time the ICBM programs started in 1955 (also true). Ultimately this was because the necessary technology was beyond the technology of the day. Finally, I said that I was only discussing ballistic missiles anyways, so the cruise missiles are irrelevant.