These are good and valid points all.
There is at least one "ATC-system project" that took at least
10 years to be completed, that I know of. There are some other projects
that never got to the completion phase.
And who knows every line of the programming code for sure?
Aviation is a special "art" because it needs so much back-up systems.
Almost all the systems are at least backed up with a secondary system
sometimes with a tertiary system. And so on.
It is quite wonderful how easy it is to increase the safety (i.e. "redundancy")
with adequately trained, highly qualified, personnel.
If it happens one day, let's say, in fifteen years that the computers took
some tasks from humans to "ease the strain", then there most likely will
be needed human interventions and "human touch" to control and
monitor those very systems. And the men and women in the ATC
are the ultimate fail safe network. When adequately trained and given the
chance for high quality rest etc.