Looks interesting. We’ve picked tools based on time saved without too much extra knowledge or overhead required, so this may prove promising.
NX is good because it does the caching part of CI in a way that works both locally and on CI. But of course it doesn't really help at all with the other points raised by the OP.
One interesting thing about NX as well is that it helps with you managing your own local build chain, like in the example I mentioned above, when I run a project that requires the C++ native dependency, that project gets built automatically (or rather my computer pulls the built binaries from the remote cache).
But for all of this to work you need to set up these dependency chains explicitly in your NX configuration, but that is formalizing an actual requirement instead of leaving it implicit (or in Makefiles or in scripts that only run in CI).
I do have to say that our NX configuration is quite long though, but I feel that once you start using NX it is just too tempting to split your project up in individual cacheable steps even if said steps are very fast to run and produce no artifacts. Although you don't have to.
For example we have separate steps for linting, typescript type-checking, code formatting, unit testing for each unique project in our mono-repo. In practice they could be all the same step because they all get invalidated at the same time (basically on any file change).
Our NX is pointed to store artifacts in GHA, but our GHA scripts don't do any caching directly, it is all handled by NX. It works so well I would even consider pulling a nodejs environment to run it in non-nodejs projects (although I haven't tried, probably would run into some problems).
It is somewhat heavy on configuration, but it just moves the complexity from CI configuration to NX configuration (which is nicer IMO). Our CI pipelines are super fast if you don't hit one of one of our slow compilling parts of the codebase.
With NX your local dev environment can pull cached items that were built from previous CI ran-jobs or other devs. We have some native C++ dependencies that are kind of a pain to build locally, our dev machines can pull the built binaries built by other devs (since all devs and CI also share the same cache-artifacts storage). So it makes developing locally a lot easier as well, I don't even remember last time I had to build the native C++ stuff myself since I don't work on it.