>Fortran and C started trying to do everything and they failed
You have an interesting definition of failure.
You have an interesting definition of failure.
And C got the floating point operations B did not have, and was actually used for lots of numerical work for a while (and it still is, up to some point), but nobody was totally happy with it so we got C++, new Fortran versions, Python, now Julia... Although it always is an option due to the availability and quality of C compilers, I would not say that C succeeded in becoming the language of choice for scientific computing.
Of course, this does not mean that C or Fortran are failures.
So, "at least one operating system programmed in Fortran" doesn't counter "Fortran hasn't been really used for systems programming", if that operating system is some irrelevant research project, or (as in here) a commercial niche system, that maybe ever reached 0.00001% of the OS users space.
The first section of the linked article says that Fortran "was an odd choice from a pure computer science standpoint", that they "developed hardware optimized to run FORTRAN", and that large parts of the OS (in particular, the kernel) were eventually rewritten in other languages.
This is, in my opinion, a great example of how Fortran could not compete with C as a systems programming language.